Tactics

"Stick together!"

- Francis "Now nobody wander off!"

- Ellis

Assuming a certain level of basic skill and familiarity with tactical shooters, these Tactics should help you and your fellow Survivors get through Left 4 Dead... alive! As a start, make sure you know all of the Controls.

Above all else, no matter which team you are on, the Infected or the Survivors, in the end you will be depending on the people around you to survive as well as to have an overall good experience. This game requires cooperation on all sides, so be kind, treat others nicely, don't go overboard with the trash talk, do not belittle your teammates and be patient with the less experienced players. With luck, they will return the favor.

General strategies
In-game, Survivors usually play through following certain main strategies; note, however, that these strategies are suggestions, not obligations, particularly in chaotic or critical situations. Survivors should still keep in mind what they are doing and get back to formation when such situations end.

These are the main strategies that Survivors use in game:

Sweep and Clean
Survivors stay together, travel through the map while taking out any Infected they meet, aside from Witches that can be avoided. When running past a room or space on the side of the path, Survivors either ignore it and run past, or send in 1 or 2 Survivors to search for supplies and kill the infected inside while the others guard the entrance.

This strategy is used most commonly in Campaign when traveling through the map on easy difficulties, as the horde and Special Infected are not so dense and are less threatening.

When using this strategy, it is best for Survivors to have a balanced weapon formation. Pistols, hunting rifles and sniper rifles are effective when clearing the field and saving ammunition while other weapons can be used to deal with Special Infected and hordes.

Rushing
Survivors stay together, travel through the map and head toward their target quickly, ignoring Common Infected that aren't hindering movement. Special Infected may be left behind or ignored if not posing an imminent threat. Rooms on the side of the path are usually ignored unless the Survivors have low health or lack supply.

This strategy is used most commonly in Campaign when traveling through the map on hard difficulties, Versus, Scavenge, during gauntlet crescendo events, heading toward the rescue vehicle in finale, or when Survivors need to reach a resupply point or more secure location. Since the horde and Special Infected are dense, the risk to clean up and scavenge for additional supplies is higher than the possible benefit. If any Survivors are incapacitated, the rest of the team either stay together to help them up while defending, or leave them behind and continue toward their target.

When using this strategy, it is highly advised for Survivors to use shotguns, automatic weapons and melee weapons. Hunting rifles and sniper rifles are ineffective as Survivors won't have time to stop and snipe, while pistols are only used to deal with low quantity of Common Infected or as a back up long range weapon for shotgun users. Ensure that you have some method of spawning a horde (e.g alarmed car, Boomer bile). This is because when either one occurs, the Director will redirect idle Common Infected at a specific spawn point, which can be delayed further with Boomer Bile. Common Infected will not spawn as you progress because of a set limit that can be on the map at one time, and because those Infected are doing an action which prevents the Director from spawning them near the lead player's location.

In a Campaign situation, rushing should only be used if a Tank has already spawned earlier on in that level. Otherwise, players run the risk of having to deal with both the Tank and the horde at the same time, which can spell doom. In addition, bots can lag behind shooting the Infected and if you are caught by a Special Infected, can result in your death as the bots attempt to reach and rescue you.

A melee weapon is also advised while rushing, in the event that pursuing Infected catch up to you. Melee weapons are far more effective then pistols in close range combat and using a pistol can result in unnecessary damage.

Hole up
During a horde, crescendo events, or in 1st and 3rd finale waves, Survivors do not typically attempt to advance, but instead "hole up" in a relatively defensible location to face the incoming horde. Survivors stop moving forward and stay put until the horde is over or they are low on supplies, in which case the Survivors switch to the rushing tactic to head toward the supply spot.

The key to the success of this strategy is to limit the directions from which the Infected can reach the Survivors, permitting survivors to focus fire on choke points, increasing accuracy and taking advantage of piercing damage.

Suitable location for this strategy include small rooms with few doors and windows as well as elevated positions with few approaches and good sightlines.

When using this strategy, shotguns, automatic weapons and melee weapons are highly advised, while hunting rifles and sniper rifles may also be useful if other Survivors can defend the user very well.

For more information, check the "Fighting the Horde" section.

Surrounding
When facing a startled Witch or a Tank, Survivors are in the defensive but cannot stay in one place. Instead, the Survivor being targeted keeps walking backward, facing the incoming infected to keep attacking them, while other Survivors move around left or right to surround the target. If the Witch incapacitates her target, the rest of the Survivors move up close and kill her while helping the victim back up. If the Tank incapacitates his target, another Survivor draws his attention while others revive the victim.

Opening space is very important for this strategy. It not only helps the Survivors surround the target while keeping their distance, but it also allows them to spread out to avoid blocking one another's lines of fire. Therefore, Survivors will usually backtrack to find an opening space when using this tactic.

When using this strategy, it is advised to use shotguns if the Survivors are willing to be targeted and want to fight in close range, while those who want to provide firepower support should choose automatic weapons. It may be difficult to make the target follow the Survivors' plan. Hunting rifles and sniper rifles are not advised due to their low firing rate, pinpoint nature and low accuracy while moving.

Fighting the horde
Common Infected run fast, come in large numbers, and are often backed up by Special Infected. This section describes tactics you can use regardless of what your teammates are doing.

Readiness is all
Before the Crescendo event, Gauntlet Crescendo event, Finales and unavoidable panic events, make sure you and your teammates are ready, and if possible or necessary, make a plan before starting. Especially on higher difficulties, unprepared teams are much more likely to be devastated by the hordes of infected.

Doors and corners
Always close doors when you find them. You can then safely kill Infected through the door. If the hole in the door is big enough, go ahead and use melee through the door. This will knock the Infected back, saving the door from immediate destruction, and keep you nice and safe. But also remember this can work both ways as good Smoker players will grab Survivors through the hole in the door, and Spitters can spit through the hole on the door, while the rest of the group is looking in the opposite direction thinking that it's safe to be behind a door.

Closing doors behind you is also useful while you are moving through a level. The AI Director is notorious for sending Infected to you from the direction you just came, and those surprise Infected can slow, injure and separate your team. Shutting doors that you just came through can slow down those sneaky Infected, and might mean the difference between incapacitation / death and survival. It is especially useful to shut doors in the finale of a campaign which can make defending them a great deal easier.

However, a Tank or a Witch can destroy the door with a single hit. It is advised to open the doors before fighting them, this not only saves the door so they can be closed after the fight is over, it also prevents Survivors from getting stuck, or have to turn around to open them during the fight.

When a room gets thick with Infected, the best cover in this game can be found in a corner, or a wall to your back. You can then meleeshove to knock back Infected and shoot when you have breathing room.

Contrary to popular belief, fire extinguishers do not damage either the Survivors or the Infected. They also do not start panic events. Therefore, they should not be factored in when you are deciding where to fight a horde from. However, fire extinguishers have a similar effect to the shoving, so setting them off by shooting through a damaged door to push back the horde can be quite effective, especially when the Infected are in a bottleneck.

Although closed doors are an advantage, keeping doors open can also help the Survivors. The Survivors can then proceed to fight the hordes without running the risk that the door will be destroyed by the Infected. That way, the door can simply be closed, stalling the Infected and giving you time to heal or even resupply if possible.

However, many Human-controlled Infected in Versus tend to go through the level ahead of the Survivors, destroying all of the doors. That makes it easier for the Horde to rush at and attack the team of Survivors, and makes defense more difficult. However, to use this tactic the Special Infected must spend valuable time attacking the doors, during which there will only be three Special Infected attacking the Survivors.

Choke points
A group of Survivors can survive the Infected horde if they use a narrow opening to draw the horde to them. This creates a slower flow of Infected, and allows the Survivors to concentrate fire-power all in one direction, making their defense more successful. Examples of effective choke points are:


 * A narrow hallway.
 * A secure room with only one entrance.
 * A slim rooftop with only one pathway to the Survivors.

Effective choke point tactics include two rows of Survivors near the choke point entrance, where two Survivors are crouching up front - usually with shotguns - while the other two Survivors stand up in behind and shoot over the front Survivor's heads. Crouching Survivors can either shoot, shove or use melee weapons and can cover each other while their partner reloads.

Choke points can be a problem when Survivors forget that a room isn't secure from all locations - this leads to surprise zombies breaking in from another point (like through a wall or a ceiling) and overwhelming the Survivors.

Choke points are harder to find in outdoor environments, but you can always use an entrance of a building while inside to fight Infected while they try take on your group.

Other issues include Special Infected taking advantage of the tactical situation. Fortunately, Boomers and Hunters can be quickly dealt with. Chargers and Spitters force Survivors to move out in the open or all get bowled down or covered in progressively more damaging acid. Smokers require Survivors to be aware of their tactics, and they must prevent their teammates from being pulled away too far, or the choke point tactics fall apart rapidly. Choke points can work against Survivors when dealing with Tanks as the Survivors are boxed in and can't use their superior speed to their advantage.

High Ground
High ground has been recognized as incredibly important for defensive tactics in real-life military strategy. Similarly, the utilization of elevated positions is an important strategy that should be remembered in-game in defensive situations.

Higher positions give the advantage of time; the infected take longer to reach the survivors because they are forced to climb up to them. During this time, they are either nearly still (if they are climbing either a short or medium distance) or moving in a straight line (if they are climbing to a significantly higher position). Both of these forms of movement are much easier to track than the normal zig-zagging pattern that infected move in while running towards players on level ground.

Additionally, high ground gives the Survivors an unobstructed view of distant areas. This gives them advanced warning about incoming Special Infected, who can often be dealt with before they become a threat. The delay imposed upon Common Infected while they climb makes the task of keeping them at bay much simpler, often requiring only two or three of the Survivors' attention. This leaves one or two Survivors who can focus on killing bigger threats before they reach the Survivors.

When dealing with Common Infected on high ground, keep in mind that it is entirely possible to knock them off of your high platform to give yourself breathing room. It will take a much more significant amount of time for them to reach you again than if you were simply knocking them back on level ground. If you keep shoving infected off of your defensive position while you reload, you will probably remain unharmed, even if you aren't receiving support from teammates. Once reloaded, you can resume killing the infected that you left alive during your reload.

Sadly, being on top of a car, subway cabin or other small object is of negligible value as defense in this game due to the climbing abilities of the Infected. Because the infected can climb up from any part of a small elevated surface, unlike higher cover where infected can only climb on certain parts of the structure, you will likely be completely overwhelmed by a crowd of infected surrounding you.

Additionally, a group of Survivors all defending a high ground point using both melee and fire-power can really slow down Infected's ability to disrupt a staged defense. Working together is key in high-ground defensive positions. During finales especially, you should find the high ground and defend it until the rescue vehicle arrives.

Special Infected first
During a horde, Special Infected are still more dangerous than Common Infected. Hunters, Smokers, Chargers, and Jockeys can seize one Survivor, which not only make the Survivors short one gun, but also make the victim a sitting duck to the Common Infected around. Boomers can extend the panic. Spitters, Tanks, and startled Witches can cause chaos and take chance to do more damage during a horde. Survivors should try to seek out Special Infected during a horde and take them down first, especially when they are about to attack or have already pinned a victim. If the attack from Common Infected hinders your aim, shove them back, use a Pipe Bomb or Bile Bomb to lure them away, or use an adrenaline to disable the stunning effect. Scoped rifles are best at doing this task, although sub-machine guns, assault rifles, and grenade launcher can also do. However, if the infected are completely overwhelming the Survivors, the use of shotguns or automatic weapons to cut a hole in the Common Infected to the Special Infected target may be more effective.

Protecting teammates
As long as there are other Survivors, Common Infected may choose to attack them instead of you, depending on their weapon, status, and skill, the teammate may be capable of holding on their own without needed attention if they are in good condition, but also may be prone to attack, such as being pinned, incapacitated, or covered in Boomer Bile.

Aiming skills is needed to support teammate as much as possible while minimizing friendly fire damage. An automatic weapon or sniper rifle can easily mow down Common Infected that are surrounding a fellow Survivor without friendly fire if aimed well. Weapons with large spread or splash damage, such as shotguns or explosives, are poor choices, and can easily cause more chaos as the Survivors being helped try to react to the unexpected attack. Asking the rescue target to crouch allows you to shoot above them. Shooting through objects is also an option, as bullets pierce through anything will not deal friendly fire damage.

Throwables also work if used well. Pipe Bombs and Bile Bombs can easily lure the entire horde away (In Bile Bombs' case, the Survivors cannot be covered in Boomer Bile.) While Molotovs can block and burn down an entire horde, it only works if the horde is still on their way, and will cause friendly fire damage if a fellow Survivor is in its exploding proximity.

Melee weapons are another choice, while its large sweeping area means Survivors will likely to accidentally hit their teammates a few times, its friendly fire damage is minimal, and its large sweeping area means the horde will be cut down very quickly. Friendly fire damage taken will be far less that the potential damage the horde can dealt.

Alternatively, a bottle of Pain Pills or an Adrenaline Shot can be given to help teammates deal with Common Infected more efficiently if in bad condition.

Interestingly, on lower difficulties, due to low friendly fire damage, weapons with large spread or splash damage can actually help clearing the Common Infected easier, while the friendly fire damage is smaller compared to the damage from the horde. Even a Molotov to the feet can give great aid if the Survivor is still standing and has high health. It is advised to communicate with the others whether they need help or not, and what you are going to do so they can do their best to reduce friendly fire damage taken.

Heavy Water
In Left 4 Dead 2, you will encounter waterlogged areas in three of the six campaigns (one of which is DLC, and not including custom made campaigns). Such areas will slow you down considerably, making it hard to navigate through the hordes of infected. It will also make dodging most Special Infected harder. However, you can improve your chances of success by Crouching through the swamps. You will still move at the same speed, but your accuracy will improve. Lower to the ground means that you can also see Mud Men easier. Otherwise, try to avoid swamps whenever possible.

High Cover
High ground or a building with stairs or ladders can be quite effective when dealing with the infected. When they attack, survivors can take many of them one by one. Additionally, in campaign mode or other modes, you can protect your teammates from being overrun. During a campaign, especially in finales and survival, always go to the high levels of the building if possible. But not that high when fighting a Tank because in No Mercy Rooftop Finale, he can punch you of the building, resulting instant death.

The disadvantage of this tactic is that if the survivors stay in one place for too long, a Tank can still throw concrete slabs at you and a Smoker can bring you down to to ground level. This passive tactic may also turn out bad when your team is making a rush for the rescue vehicle in Finales or abandons its position. If you have to bail out, try to throw explosives that might slow down the infected while you run out of your spot.

This can be used as an advantage to the infected in some cases. Refer below.
 * A Smoker can pull unexpected survivors from afar without worrying too much to kill
 * A Hunter can ambush unprepared survivors, slowing to team down.

Charger
A Charger must be dealt with carefully, no matter the difficulty. Even on Easy, the Charger can deal a lot of damage.
 * If a Charger spawns, try to avoid narrow choke points whenever possible. A well-timed charge by a Charger can knock the whole team for 15 damage and allow the Charger to deal more damage on whoever he has pinned.
 * When possible, try to force the Charger to charge, so that it wastes it and stumbles, allowing the team to take it down before it can start meleeing the team.
 * Never attempt to kill the Charger with melee weapons after it fails a charge and stumbles, as it can still melee and result in unnecessary damage to that player.
 * Be aware that not every Charger, be it computer or player controlled, will charge as soon as possible. They may choose to use their damaging melee attack instead.
 * Don't back up if this happens, as computer controlled Chargers may instantly charge if you try to back away.
 * Be aware of your surroundings. If a Charger hits a tight-knit group in a high elevation area, this can result in some of the team getting killed by freefalling.

Spitter
The Spitter is also a dangerous Infected, especially in tight areas.
 * A Spitter does not have a lot of health, so a few shots from any weapon can kill her instantly.
 * If a Spitter spits, your character will warn the others of this. The Spitter will always spit at whoever she spots first when she "attacks", so this can be easily avoided as the spit takes 2 seconds before dealing damage.
 * If you are in the way of the spit, you will be momentairly frozen for a second. Immediately move out as fast as possible.
 * If you are caught in the spit, get away from it as soon as possible. This can be problematic if a horde is surrounding you, as you will take heavy amounts of damage the longer you are in her spit.
 * When the Spitter dies, she will leave a small pool of acid around her corpse. Wait for the acid to disappear before moving further down.
 * Never try to go around a Spitter's acid, as appearances are deciving and you will take unnecessary damage trying to go around it in a narrow area.

See also: The Infected

The Survivors
Useful Precautions:
 * Listen for the heavy breathing, gagging, and burping sounds.
 * If captions are on, make sure you know what they mean. When the Boomer "rages", it has spotted you. When the Boomer "falls", it has fallen from a higher area. When the Boomer give a "warning", it is in puking range of you.
 * If you hear one, keep an eye out for defensive positions. That way you'll be ready if the Boomer blinds you.
 * Avoid being too bunched up with the other Survivors. There's no sense in all four of you getting puked on at once.
 * On Expert, Boomers will often claw Survivors they have vomited on, dealing even more damage.
 * On Expert, finding and killing the Boomer before he can vomit or explode is incredibly crucial as the Boomer bile attracts the horde, which on expert difficulty is extremely dangerous.
 * Be cognizant of blind corners, overhangs, and obscured (i.e. wooded) areas where the Boomer may be lurking to get the drop on you. Try to give these areas a wide berth whenever possible. If you hear a boomer but can't see it, it might be a good idea to fire a couple of "blind" shots into any unseen areas in the chance of hitting the low-hitpoint Boomer.
 * In Campaign mode, Boomers will explode when they take fall damage, so watch for rooftops or windows above the ground level since Boomers will try to jump out for a kamikaze attack.

When the Boomer is sighted:
 * If the Boomer is too close, it's a good idea to hit shove it, which will push it back to some degree, then back away to a safe distance before shooting or you'll get covered in bile, even though you weren't vomited on.
 * Hiding behind something or running away when it's vomiting makes it harmless for some time and may even force it to rush at you clawing.
 * Only if the Boomer is sufficiently far away from both yourself and all other Survivors should you shoot it.
 * In Versus, before you shoot a Boomer, see if it's just staring at you, or if there are crying sounds coming from the Boomer's direction. It's possible that the Boomer is concealing a Witch, so hold your fire.

After being vomited on:
 * Know that a massive horde will immediately descend upon you and any others who have been slimed.
 * Hold your fire! Since you can't see, friendly fire is the most likely result. Shove instead, until you're sure that you won't harm your teammates.
 * Immediately find the nearest defensible corner and keep your crosshairs aimed at any open doorways, or other locations Infected come from.
 * This is not a good idea to kill the Boomer once you are blinded unless you can shove him off at safe distance or are away from your team. The explosion will make you stumble and will likely cover any missed teammates in puke as well as resetting the blindness of every teammate.  However, if you are away from your team, stumbling a bit before the majority of the horde descends on you isn't as bad as being clawed multiple times by the Boomer.

Helping a slimed Survivor:
 * Stay close to the stricken Survivor.
 * Help shove the horde back or shoot if the blinded Survivor stays safely crouched.
 * Help the stricken player to safely get to a corner to protect him from the horde.
 * Throw a pipe bomb to distract the horde (it is bad to throw a bile bomb as the horde will ignore it, thus leading to the useless waste of a precious item).
 * Stay out of the biled Survivor's way: they may mistake you for a zombie and shoot you, which could be disastrous on hard difficulties. If they are swinging their melee wildly, it is very easy for them to accidentally hit you unless you're a bit away.

The Infected
As a Boomer, your job is to slow the Survivors down by attracting the horde. The Director will spawn one horde for each Survivor vomited on for a maximum of four. As a Boomer, you will need to hide and ambush Survivors since Boomers have the lowest amount of health, and emits a lot of loud burping and gurgling noises. The Boomer acts more like a support class, as they don't dish out much damage on their own. Due to this restriction, they excel when placed at the start of any coordinated attack. Their main attack attracts the horde, causing Survivor teams to panic, which creates ideal opportunities for the other Special Infected to move in and deal serious damage, and also blinds survivors, giving special infected a chance to carry survivors away from teammates unnoticed. Remember that you have very low health and will explode in only a few shots. If you try to rush at the Survivors in the open, they will simply kill you before you get within vomiting range.

Another weapon of the Boomer is that it explodes when it dies and covers any nearby Survivors with bile, which has the same effects as vomit and also causing them to reel back. This explosion is a good way to cover any Survivors you missed because inexperienced players have a tendency to shoot on sight instead of using a melee attack to knock it back to a safe distance. You can vomit on unsuspecting Survivors below with impunity if attacking from rooftops. Then jump down to let them shoot you in blind panic, if your health is low enough or you are high enough up you can instantly explode as you land covering any nearby Survivors! Exploding on a person who is already covered in bile does not spawn another horde, so you should either retreat until you're ready to vomit again or to get as close to the other Survivors as you can in the hopes that they'll cause you to explode bile onto other Survivors.

Take advantage of blind corners, overhangs, and obscured areas (such as woods) when choosing where to strike the Survivors. Such areas increase your chance of success, as they allow you to get closer to the Survivors before they have a chance to kill you.

Experienced Boomer players can use the knock-back effect of the explosion very effectively by knocking Survivors off high ledges doing large amounts of fall damage, if high enough, cause instant deaths or incapacitation, or causing them to cling to the ledge and need to be pulled up. As a Boomer, claw at Survivors if it doesn't look like you can escape or if you want to explode and knock the survivors back.

If you explode near a car with an alarm, this will set it off. So if you can, quickly go vomit on the Survivors, retreat near a car alarm, and allow yourself to explode setting off the alarm and spawning another horde.

In some situations, it may be possible to kill a Survivor that has become separated. This is achieved by sliming them, then clawing them. The boomer is able to knock Survivors to the ground, leaving them vulnerable to attack. This technique leaves the victim no room to breathe and they will be quickly incapacitated, and the dense horde will hinder the attempts of their team-mates to revive them. The hoard also does 10 damage per hit to incapacitated players (not changed very much based on difficulty), so the infected only need to hit the survivor about 26-28 times (accounting for normal health loss) before they kill the survivor.

Fire may also be an effective weapon for you. A Boomer that is lit on fire effectively becomes a "ticking timebomb", and once its health is depleted it will explode, covering any nearby survivors in Bile.

The Survivors
When dealing with the Hunter, there are a few rules of thumb and things you need to keep in mind:


 * Always have at least one buddy close at hand.
 * Listen for the distinctive growl the Hunter makes when he is crouched and ready to pounce. Once you hear the cues, remind the other Survivors of the Hunter's presence to keep everyone on their toes. This may sound useless, but it often prevents Survivors from taking unnecessary damage from Hunters.
 * Remember that the Hunter won't always pounce as soon as he sees a Survivor, be it an Survivor Bot or a player-controlled one. Even the Bot waits and bides its time. As a Survivor then, your focus should be on progressing, not finding and killing the Hunter. This is especially true in Versus, where Hunter-players will often simply fly around the map with the hope of distracting and delaying inexperienced Survivors.
 * On higher difficulties, and in Versus, the Hunter will often use their claw attack instead of pouncing the Survivors. This attack can be devastating, because oftentimes Survivors will not realize that a Hunter is present until it is too late. The Hunter emits no sounds while standing, and in larger hordes it tends to blend into the crowd. As a Survivor then, it is critical to watch your team's health meters during large horde attacks. If someone's health meter drops unusually fast, it is usually an indicator that a Hunter is attacking nearby.
 * When a Hunter is growling, this means that he is ready to pounce. It is easy to cause head-shots on him and kill him instantly. If he gives off a loud screech, he's spotted you and can pounce you (only when he's pouncing)
 * If the Hunter is outside pounce range, open fire. Head-shots are particularly effective.
 * Otherwise, shove just as the Hunter starts his pounce. This will knock him back with a stun, and allow finishing him with your choice of two additional shoves or weapon fire.
 * If you manage to stop the Hunter mid-pounce, keep hitting him as this keeps him from doing anything. Definitely use this tactic when he is close to other Survivors to avoid friendly-fire.
 * Be very careful when attempting the above tactic. An Infected, AI or otherwise, can still claw you while it's stumbling backwards. This is extremely dangerous on Expert difficulty where any Infected's claw attack can cause massive damage, especially the Hunter.
 * In Versus mode, be very careful of the Hunter or any other Special Infected visible standing behind red, alarm-triggering cars, the Survivors might be tricked and lured to shoot them.
 * AI Hunters will jump if shot at, pouncing or not. This leaves them vulnerable to attacks as they can't move until they land.

Once a Survivor is pounced:
 * You will receive a visual notification that a fellow Survivor has been pounced on.
 * Shoot at the Hunter if you are far away and melee it if you are close to it, friendly fire does not hurt a player while they are pinned down (although once the Hunter is off, they are then vulnerable to such).
 * If too far away and there is no Survivor closer than you are, go ahead and shoot.
 * Be careful if the Hunter is on fire, as they do more damage, and can bring down your health very fast.
 * A head shot with a shotgun or a sniper-type rifle will kill a Hunter in one shot.
 * Don't let walls stop you. If the only way to save a fellow Survivor is to shoot through a wall or ceiling, do it. A hunting rifle is particularly effective at this, although even pistols can punch through.

The Infected
The Hunter excels at picking off any stragglers or lone Survivors in any team. A Hunter's pounce pins a Survivor, leaving the victim completely helpless and doing the quickest damage to a survivor of any infected (except the charger, if the player is not incapacitated), until the other Survivors melee the Hunter or effectively kill it. Otherwise, without another Survivor's intervention, the pinned Survivor will die.


 * Due to the fact that the majority of players travel together, Hunters will not commonly find stragglers. This behavior by the opposition means that Hunters generally cannot successfully initiate an attack and cannot expect to do serious damage. As a result, Hunters are best sent in during a Panic event, when Survivors are blinded by vomit or bile, or any other cases in which the Survivors' attention is focused elsewhere. This lack of opportunity means that Hunters must stay stealthy and hidden until opportunities present themselves.
 * In order to pounce, Hunters must remain crouched for a limited time. However, being crouched makes the Hunter growl loudly, broadcasting his arrival on the scene to any nearby Survivors. Also, whenever Survivors are in view of any of the Special Infected, the Special Infected will emit auditory sounds, such as aggressive growling in the Hunter's case, though Hunters are silent when standing still and not crouching, a trait unique only to them. To avoid this, Hunters should remain standing and out of sight until they are ready to attack.
 * One of the Hunter's best attacks, that is infrequently used, is a straight claw attack by the Hunter in a standing position. This attack can deal a large amount of damage in a short amount of time. It is much less noticeable than the pounce attack allowing a slightly longer time to deal damage. This attack should be used if the group is bunched together facing in the opposite direction or during the confusion of a Boomer attack. An advantage to this method is that the Hunter does not shriek. This allows being stealthier and easily mistaken as one of the Common Infected. Another idea is to use this attack to quickly incapacitate a Survivor in the red; one or two hits and they'll be on the ground.
 * Another effective tactic is to continuously wall jump. Hunters emit a distinctive scream during flight. An experienced wall-jumper can effectively distract a team, slowing them down, and buying the Infected players additional time, which may cause the Director to spawn a Horde. Also this can be used to tempt someone to stray away from the group to kill the Hunter. Then when he is alone, pounce on the lone Survivor.
 * If you do not rely on your teammates hunters (and Spitters) can go solo, stalk the Survivors by having them in range and sight, when the time is right, jump in and cause massive damage.
 * Hunters work significantly better with a meat shield (the horde, Charger, Tank).
 * You can insta-pounce without crouching by backing up into a wall and while still backing up, jump. You can then jump off the wall as you would a regular wall-jump. Obviously this is useful for not giving yourself away, but also extremely useful for making quick escapes if shoved off a Survivor. This has been confirmed in both L4D and L4D2.
 * If the Survivors don't seem likely to spread apart, you can try to inflict damage with high damage pounces. If a Hunter pounces from high enough and far enough away, the survivors will be slammed into the ground harder, inflicting up to an extra 25 damage if the pounce connects.
 * A Hunter's pounce can stumble any survivors nearby. This can be used to push them off a ledge and force them to hang or even push survivors into traps such as fires or a Spitter's acid.

The Survivors
Here are some basic tactics to help you deal with a Smoker:


 * When you or one of your teammates hear a Smoker, stay close together and watch out for each other. If any of the Survivors are alone and too far away from the group, they make an easy target for the Smoker. If the lone Survivor is grabbed, it's possible the other Survivors will not notice or will be too far away to help in time.
 * If a Smoker is on a roof and has grabbed a teammate then do not waste your time killing the Smoker and just shove the Survivor. The Survivor will automatically be freed. This is only recommended if you plan to weave through the map, as a Smoker that lasts longer in-game will be more dangerous over time, especially if you bump into a Tank.
 * If you see a Smoker and you're near a wall, hide behind the wall if the Smoker is in front of it. This will stop him from snaring you and you can shoot back on him as this restarts his timer on ensnaring you.
 * When a Smoker chokes a target, they are very easy to kill. A few shots from any weapon kills them easily.
 * Smokers tend to attack from behind or above your location, but some will spawn in front of you, so move carefully if one spawns.
 * When a Smoker grabs you, you will have a few seconds to free yourself by shooting the Smoker. If you are not currently holding a gun (or have started reloading) at the time you are grabbed, you will probably not have time to save yourself.
 * If a Smoker grabs you while you're throwing a pipe bomb, and no other Survivors are around or notice you, throw the pipe bomb at the Smoker. The resulting explosion will free you from the Smoker's grasp.
 * If you have a Chainsaw, when you are grabbed by the Smoker, use it to free yourself.
 * Smokers are extremely dangerous on Expert, dealing 40 damage per hit when constricting a Survivor. It should be imperative to save constricted teammates immediately, even if you will take damage from Common Infected. Left unchecked, a Survivor at full health will be incapacitated in 3 seconds and die in 8.
 * However, a survivor being dragged toward a Smoker will not take damage as often as a fully ensnared Survivor.
 * If this happens while Common Infected are attacking you, face the game camera away from the direction of the Infected. Even though you may still be dragged, if done properly you will be taking less damage from them, especially on harder difficulties where health is extremely important.
 * If you know where a Smoker spawns, "force" it to ensnare you. Once the Smoker sends out his tongue (he will also make a loud sound when he does this), immediately hide. The tongue will be unable to follow you and leave the Smoker helpless for several seconds, which should be more then enough to kill him before he manages to hide.

The Infected
As a Smoker your job is to ensnare a Survivor and separate them from their friends.


 * Your tongue attack leaves Survivors helpless after about two seconds of being ensnared. A seasoned Survivor with quick reactions can break himself free from your tongue and kill you most of the time. However, a well placed attack in the midst of a horde rush can spell disaster for the Survivors if not dealt with properly. Always look to be either up high or in a dark place as the darker or higher you are the less chance the Survivors will be able to shoot at you, and add the possible effect of common infected hitting the Survivor while he's smoked, a sort of Piñata effect.
 * An experienced Survivor can recognize the wheezing and coughing of a Smoker and will be alert and ready to save his teammates from being snared. If you want to be a real burden to the Survivors, stand in front of or behind an alarmed car. If you stand by the car and pull a Survivor over to you, the other Survivors will have no other choice but to try and save the person you snared. Generally, instinct will override common sense, and the Survivors will open fire, inevitably activating the car's alarm. Any stray bullets that impact the car will set the alarm off, attracting the horde, and buying you more time to attack.
 * This tactic also works similarly well with the Witch.
 * Good Smoker players excel at using the environment against the Survivors - this can be done by dragging them down from a higher part of a level as the fall will do a lot of damage, and in some places it will cause death. If the lower area is just where the Survivors have had to climb up from, the Smoker's target will have to climb back up to the higher area leaving them away from the group and slowing down the team. Smokers can also drag Survivors through fire that again causes large amounts of damage while either forcing another Survivor to run through the fire to release their constricted teammate or wait until the fire dies down while the Smoker does damage to the constricted Survivor.
 * In the Dead Center Hotel level, the fire in the middle of the room next to the area with the saferoom does massive damage and has debris to keep the survivor from being pulled through it to you. Hazards such as this can be useful to quickly kill a distracted Survivor during a horde.
 * Combine the abilities of you and your teammates:
 * - Smokers can drag a Survivor through a horde, creating a passage. The same passage can be used by a Charger to scare off the Survivors who rush to help their ensnared ally.
 * Smokers can also be used to position a survivor in front of a window, so a Charger can ram the Survivor off and instantly kill him.
 * - If you manage to drag a Survivor away from their team, urge a Spitter to spit or a Boomer to vomit on the Survivor you are choking to speed up their loss of health.
 * The boomer bile would be especially helpful, since the Smoker does very little damage to incapacitated Survivors and the zombies do 5 times more damage than normal to them.
 * - As always think like a Survivor, imagine the worst possible scenario, and make it happen!

The Survivors

 * Use your melee (secondary attack) to knock Jockeys off. They will be stunned so you can shoot them.
 * Keep moving so you are a difficult target to pounce on.
 * Watch the rear or front stragglers for Jockey attacks.
 * If available, use a grenade launcher (not the best idea on Expert). It will knock the Jockey off in a stumble, much like a shove but more damaging (to both the jockey and survivor).
 * Head-shots deal heavy damage to the Jockey. Shoot them by angling your gun a little down or crouch shooting them. If they get close, spray them with gunfire.
 * If a Jockey gets close, move back and then melee it. Moving back will prevent the Jockey from riding you and meleeing it will stun it and allow you to kill him. Be warned that he can still claw you while doing so.
 * Jockeys do very little damage to survivors over time, but are still dangerous if you let them carry your teammate off.  Don't worry about saving your teammate right away if they are very low on health; the jockey can only incapacitate them and start clawing.
 * However, prioritize Jockeys if there are any hazards nearby, such as fire or areas that a Charger could deathcharge the survivor off of.

The Infected

 * Your goal is to jump on a Survivor and steer them off a tall edge, into an area their team members can't get to easily, or somewhere far behind that will stall the team and damage the victim.
 * Move around a lot amongst the Survivors. You are pretty fast and can get them to shoot each other.
 * Slash with your secondary attack to decrease health while moving.
 * Once you jump on a Survivor you are a target, so try to coordinate your attacks or jump on someone who is low on health. Once you incap them you can move on to another target.
 * The Riding My Survivor mutation is an excellent place to practice Jockey tactics.
 * While riding, steer the Survivor into Spitter acid or other hazards.
 * Take out anyone with a melee weapon first as they do huge damage.
 * You can also steer a Survivor to a Witch, or hide behind her with your incapped Survivor. It will be a very hard choice for the Survivors to shoot at you.
 * A shoved-off Jockey can jump again sooner. Use that to your advantage.
 * You can also use the high buildings to fall onto Survivors from above. The best way is when the roof is just above the door. Wait for all of them to leave and then quickly fall on the last one and grab him inside. A successful attack will really slow down the Survivors.
 * Even if the Survivors are clumped together, you can still cause confusion by quickly grabbing a Survivor and steering them behind something, forcing the others to chase after you and save their pal.
 * Steering the Survivor off a cliff can slow down the team even more, and a Charger could easily take a rescuer.
 * Steer Survivors in front of high up windows that a Charger could plow the Survivor through. This can very quickly and effectively kill a Survivor, but the tactic is inconsistent.
 * If you hide behind an object that cannot be jumped on top of, move around it when Survivors chase after you. You can waste their time and health with a bit of humiliation thrown into the mix.
 * If you are high up and drop down without jumping, you will still ride anyone you land on. This can be used in the same way a "Rocket Boomer" is used, by running forward, jumping and spawning in mid air, and launching yourself at the Survivors, landing on a head and riding them into the sunset. Though difficult to do, this tactic certainly wouldn't be expected.
 * Use Tanks as meat shields when you ride a Survivor. The Survivor is unable to help the fight, the others can't help him without going through the Tank first, and if you get knocked off, the Tank has a chance to finish the job.

The Survivors
General Tank tactics:
 * If an AI Tank is still idle (say, it is in a room raging and pounding its fists as usual) and it isn't facing you, you can still shoot it with a long distance weapon about 3-4 times until it will notice you and attack.
 * Keep your distance from the Tank if at all possible. You can't expect to survive a one on one with a Tank unless you have a decent amount of health and are an experienced player, but having to go one on one with Tanks should rarely happen. Take advantage of your surroundings by climbing up and jumping off of ledges, as the Tank leaves itself open whenever it has to climb.
 * In L4D2, the tank no longer attacks incapacitated players. Once he downs one, he will immediately change targets. On Expert, this is especially deadly as he can quickly reduce even the best teams to dust. If one, two, or even three players get downed, it is imperative to pick them back up. Have one player distract the Tank while you pick your fallen friends up. It's much easier to kill a Tank with 4 people shooting it rather than only 1.
 * Set the Tank on fire using either a molotov or a gas can. As of January 23, the damage the Tank receives from fire is now reflected in the Tank's health. This will reduce the amount of time that's required to engage and defeat the Tank.
 * Explosives such as pipe bombs, propane, or compressed air tanks are great for limited big damage, but not as effective as fire, which always does guaranteed damage over time to the Tank. Propane and Oxygen tanks will also knock the Tank back, like most other Infected after a melee attack.
 * Keep clear of cars, fallen trees, furniture, and dumpsters if the Tank is nearby. The Tank will definitely use big objects in the environment and try to punch these objects towards Survivors, which means an immediate incapacitation if said object hits any one of them. Tanks will try to climb over burning barrels, though, setting them ablaze (usually only applies to AI-controlled Tanks, but might work with some similar smart players), so moving to put a barrel between you and him will usually have the same effect as a well-placed Molotov. Make sure you run, because you do not want to be pounded on by a burning Tank.
 * Try to draw the Tank into a crouching only area. It can buy you a few seconds while the Tank tries to wiggle its way through. Good examples of crouching-only areas are ventilation grates, windows and ambulances.
 * Note however that this is no longer a viable tactic as of the latest update. Tanks now crawl at a much faster speed and will quickly overwhelm a team hiding in vents.
 * It is very effective to make a Tank go through a window, slowing it down, and when it is almost crossing it go to the other side to make the Tank slowly cross it again until it dies. This can deal a lot of damage to the Tank or even kill it leaving the Survivors unharmed. This can be done with the windows of the main buildings in the No Mercy, Death Toll, and Blood Harvest finales.
 * The Tank can climb, but it slows down. Take advantage of this as you can climb up and down much faster.
 * In closed quarters, all Survivors should concentrate all of their fire-power on the Tank. The Tank will pound on a Survivor or two, but everyone should make it out alive.
 * Another useful tactic is to get to an area immediately inaccessible to the Tank. The rafters of a building away from the area that allows one to climb up to it is effective, because the Tank wants to get to you by the shortest route.
 * Whenever a Tank takes damage, its forward momentum slows down (just like yours do when Infected hit you). If you can light him on fire, hit him with a minigun, and have the other three pump Shotguns into him, the Tank slows to a virtual standstill and is quickly dealt with.
 * Lacking a good situation, have one person focus on avoiding the Tank while the other three keep him as slow as possible. Make sure to communicate and let your bait know if he switches targets.
 * If the Tank throws a rock at you while you are strafing, immediately switch direction - the Tank throws the rock to where you'll be, not where you are.
 * It is possible to force the Tank to drop a rock by shooting the concrete as many times as possible whilst it is still in the Tank's hands.
 * On Expert difficulty, the Tank can incapacitate a Survivor with one punch or his rock throw. Once a Survivor gets incapacitated, they will die in two hits so keep your distance and stay on your toes.
 * Never let the Tank back you into a corner as you can't go anywhere, and most likely you will be taken down.
 * Explosives deal around 750 damage to the Tank.
 * If you are using a generally inaccurate weapon and/or don't like to move while shooting or to dodge a Tank's concrete slab throw, take cover in a ideally medium to big area of cover (small will do; just crouch). While you reload, head back into cover, then pop out, burst fire, then duck into cover if it throws a slab. If you see that everybody's retreating or that a horde's coming and everybody's too busy with the Tank, cover them and try to alert a player that either a horde or a Special Infected is coming.
 * It is also possible to block the way of a Tank by stopping in the middle of a ladder the Tank has to go through to damage the Survivors. The ladder has to be in a 'tunnel' where the only way out of it is either up or down, not sideways. Your other teammates can freely shoot the Tank but they have to be careful not to shoot their friend since the last thing they want is to incapacitate him and let the Tank successfully climb the ladder. This can be done, for example, in the exit ladder of the Sewer in No Mercy. This tactic works better on AI Tanks since they're usually won't jump off ladders (or do it quite late), so you will have plenty of time to pour it on.

If someone else is attacked by the Tank:
 * If the Tank is pounding a Survivor into the floor, another Survivor can aggravate the Tank and possibly draw its attention from its target by shoving and hitting it in the back. Shooting a Tank won't have the same effect as tapping it on the shoulder with your gun's butt when it's busy killing your teammate. Be aware that a Tank can turn around mid-swing and smack you if you're trying to shove him.
 * Another way to aggravate the Tank and draw its attention is to get on a nearby minigun. Even if you can't hit the Tank, he will stop pounding on the incapacitated Survivor, and go after the gunner. Another Survivor should then try to help the downed player up as soon as possible.
 * Never let the Tank back any of your teammates into a corner as they can't go anywhere and it is most likely they will be incapacitated.
 * Melee weapons deal 500 damage per swing at the Tank, regardless of what type. You can easily reduce a Tank on Expert difficulty this way, although you will need to switch from helping your incapacitated player and swinging on him as they can usually bypass this, but AI Tanks on L4D2 will always target incapacitated players if they can.
 * If you have pain pills and someone else's health is in the red, give it to them. This can prevent them from getting incapacitated. Also, if someone's health is above 40%, they can outrun the Tank. Pills provide 50% health boost so giving pills to weaker Survivors will let them run faster.
 * If a teammate is incapacitated and you don't want to change his target to yourself, you can do one of two things:


 * A) Fire away until the Tank dies, although on Expert he will most likely kill the incapacitated player before the Tank itself dies.


 * B) Run, especially if close to the safe room. If all the players can get to the safe room and close it while the Tank is killing another player, you will succeed.


 * C) If you are the incapacitated player, don't be afraid to shoot at him with your pistols. Every little bit helps. It can really mean the difference between the Tank dying on your body, or you dying under the Tank.

The Infected
The Tank, one of the most dangerous Special Infected by far, is able to withstand lots of punishment and can incapacitate Survivors in a few punches. In Versus, the Tank is given out at random but usually goes to the two players with the highest points. When you get the Tank you will usually spawn ahead of the Survivors. Start running towards them as soon as you spawn for two reasons: As a Tank, you need to use the environment to your advantage. Punching certain objects - they will glow red to show that you can punch them. Punching the object at Survivors will cause an automatic incapacitation on impact. In a choke point, such as the alleyways of No Mercy which mostly have dumpsters or cars, this can be devastating, scoring an instant win as all the Survivors are incapacitated in one hit. It's also possible to knock objects into the alleys in such a fashion that it effectively blocks the Survivors path, dooming them to a premature grave. However, if you die before the Survivors do, and their path is still blocked (e.g. if the door next to the police car is blocked on Dead Center Streets), the obstacle will only last a minute or so before it despawns and allows the Survivors to pass.
 * 1) The Tank Music will play and the Survivors will prepare for a Tank, meaning you do not have the element of surprise.
 * 2) The "Control Effect" or Frustration Meter. If you do not hit the Survivors with a rock or your fists, your Frustration Meter will go down. When it is completely gone, your control will be given to someone else. Eventually, if two or three people lose control in this way, then control will be given to the AI Director.

On all finales, after each horde spawns, a Tank will spawn. This will happen twice before the rescue vehicle arrives. Once the rescue vehicle arrives, another Tank will spawn, and that will be the Infected's final chance to finish off the Survivors.

If possible, try to punch Survivors off rooftops for an instant and free kill. Remember to always look for a lone Survivor as a Tank! If the others run off but one is trying to heal or gets trapped by Infected, score an easy incapacitation and lower the Survivor count! They won't be able to get far, but if you're running at all of the Survivors and they're all firing continuously at you, your speed will be dramatically reduced and they will more than likely kill you before you can do any real damage.

Fire is the Tank's worst enemy. If the Survivors manage to set you on fire you will eventually die no matter how much they shoot you or how many you kill. After being set on fire by a molotov/gas can, you will begin to slowly lose health. A Tank at full health that has been set on fire will die in thirty seconds, so avoid fire at all costs! However, if you are near a large body of water (e.g. at the Death Toll Finale) you can jump in and put the flames out.

Do not punch any Survivors already pinned by Special Infected, or you will kill that Infected, (unintentionally) free the Survivor and possibly save their life. Instead, aim for any Survivors attempting a rescue and give the Hunters/Smokers time to at least incapacitate their prey. Safe room doors can be destroyed by the Tank, but only the ones at the beginning. You cannot destroy the Safe Room door at the end to prevent the Survivors from winning.

Most bullets cannot penetrate the Tank. Sometimes it is useful to purposely put yourself in between free-standing Survivors and one that is pinned by a Charger, Hunter, or Smoker. Tanks are also meatshields!

Roll in and make an attempt to separate the entire team by:

1) Throwing a concrete slab.

2) Running in and hitting a Survivor (blasting them back).

3) Knocking a heavy object into the middle of the group. If you do this with a Charger, it will make your job easier.

Doing this can pretty much destroy the Survivors; but if you don't, more of your teammates will roll in as well, killing any runners.

Witch
Here are some basic tactics to help you deal with a Witch:

The Survivors

 * Turn off your flashlight.
 * Watch out for her signature red glow.
 * Note that music gets louder as you get closer, and gets quieter as you are farther.
 * Do not shoot at or near her; loud gunshots near her will startle her.
 * Advise allies if you locate her, and give them the precise location.
 * Memorize the general area. If you end up startling her, and then shoot while backing up, you don't want to fall off a building or run into a wall.
 * Try to get past the Witch; don't start a fight unless you absolutely have to, such as in Expert Mode where the startle time is too low for players to pass through.
 * If you absolutely cannot get past her, your only option may be to fight her.
 * Never startle the Witch in Single Player Expert or Realism Mode. The AI will most likely not be able to deal with her before she chases you down and kills you. Go around her unless there's absolutely no way to avoid startling her.

Defeating the Witch:
 * First, try to "cr0wn" her with a Shotgun. For best results, use an Auto Shotgun or Combat Shotgun. First is to position yourself behind her. Run right up to her, then aim at her back or head and spam the fire button. Aiming at her back has a larger area to shoot at, while aiming at her head does more damage, but is a smaller target area. If she doesn't die in the first shot, the next two or three should kill her. An alternate idea would be to place a propane tank next to her, and detonate it.
 * You can stun the Witch BEFORE she gets to move by shooting her in the head with the Sniper Rifle or Hunting Rifle. She will go down usually in one magazine of the Hunting Rifle but if she doesn't, it still gives you and your team adequate time to put her down.
 * Another strategy relies heavily on the environment: if you can quickly put a closed door and a gas can between you and the Witch, you can passively kill her without any damage to yourself. First, place a gas can on the opposite side of the door to the Witch, then shoot her. Quickly shut the door and run as far away as possible. When the Witch breaks down the door, she will destroy the can and burn herself. When this happens, she 'forgets' to attack players.
 * When using a chainsaw, it is possible to charge the Witch and kill her without taking damage.
 * Be extremely careful when trying to cr0wn the Witch or kill her with a chainsaw in Versus, as Infected players will very likely attempt to "pin" the killer (Or if very organized, pin the other three Survivors so the killer will have to choose between rescuing them and risk startling the Witch or killing her first and letting the Infected heavily damage the other Survivors). If she can't be avoided, killing her from a distance may be safer.
 * Try not to attack the Witch if there are undistracted Commons nearby, especially in Versus, as a Boomer/Hunter combo can be deadly to the killer (The Horde, Hunter and Witch all together will kill a downed Survivor in no time).

If you startle the Witch:
 * If she doesn’t die, burn her with a molotov; that way, her health will continuously deplete, as well as slowing her down slightly. The slowing effect is more noticeable on Left 4 Dead 2.
 * Run back to the safe room as she can't break down the door, then when you are safe inside, reload. This is not possible in Versus, as the safe room door cannot be closed after being opened. Witches, however, retreat upon players reaching the saferoom, either the end one or the start one.
 * DON'T STOP MOVING ! The Witch, though strong, is not slow. She is actually quite fast (300 speed compared to the Survivors' 210) and will most likely catch up to you if you stop to take a shot, so don't stop running.
 * If forced to run, use adrenaline to increase your running speed.
 * DON'T STOP SHOOTING! If you have a hunting rifle, shoot from afar; if you have a shotgun, get up close, but keep a distance. Witches tend to make a beeline on you, not moving directions to make you lose your aim, so spray her quickly with your ammo.
 * Have a trustworthy ally next to you in case she incapacitates you.
 * If possible, use heights to your advantage (Example: at the top of a ladder). That way, if she climbs to get to you:
 * 1) Her attack is delayed.
 * 2) You have an excellent chance to get some head-shots.
 * 3) You can just keep running.
 * Find a ladder if possible! Stay on it and the Witch can't attack you. This also gives your teammates some time to shoot her.
 * If the Witch is too close to you and the difficulty is on Expert, try to hang on the edge of something like a roof, giving more time for the Bots or your friends to shoot and kill her before you die. The fire can also help you in this case since you can get incapacitated.

If someone else startles the Witch:
 * Make a defensive line between the Witch and the one who startled her, and unload before she gets to them. If she is not killed, then her health will be low enough for the running Survivor to kill her.
 * If you have a Shotgun, keep shooting her up close; she won’t attack you unless you directly block her from moving (If you block her in an open area, she will just push you out of the way while charging, not causing damage).
 * Throw a propane tank at her and shoot it. This will hurt the Witch, as well as push her back a few feet, delaying her attack and sparing your teammate.
 * If you are in a tunnel or other confining space, do not stand between the Witch and her prey. She will get frustrated shortly and kill you instead.
 * On Expert, the Witch ignores incapacitation and instantly KILLS her target. If a teammate has startled the Witch, incapacitate them immediately (unless they are on their last "life). Even though the Witch can still kill them in one hit, she has a charge up delay when she attacks an incapacitated Survivor. Make sure you have a weapon to kill her quickly or your attempts will be in vain.

What not to do when startling the Witch:
 * Though it is smart to close doors behind you because it will delay Infected and Special Infected, this will not stop a Tank or a Witch. If you are being chased by the Witch, she will rip the whole door down with one attack.
 * Don't split up, the Witch will only go for one person; the others are completely safe, so if everyone runs in separate directions, the one who startled her will most likely be killed by the Witch, and the others may be killed by other Special Infected, so stick together!
 * Don't shove the Witch (if she hasn't been stumbled with explosions) -- except with the Chainsaw, and only do so if you can sneak up on her.

See the Witch for more tactics.

The Infected
Although you cannot play as the Witch, you can certainly use her to your advantage:
 * Smokers can drag Survivors to the Witch.
 * Hunters and Boomers can crouch in front of the Witch, obscuring her from the Survivors' sight. Alternately, if a Boomer dies while the Survivors are relatively close to the Witch, the explosion will startle her, sending her after the person who killed the Boomer. It is also useful to duck behind her as they will not risk trying to kill you if it would alert the Witch
 * If you pounce a Survivor as a Hunter while the Witch has already incapacitated someone and is attacking, you will not be damaged and the Survivor will die twice as fast. You will also get points for the damage she inflicts.
 * Experienced Hunter players normally crouch just out of sight near the Witch, waiting until a player runs up to attack the Witch and pouncing them just before they get a chance to fire. This gives the Witch the potential to do the most damage, possibly even killing the Survivor if timed properly.
 * Most experienced Survivor teams will have three players take up defensive positions while one goes up to "cr0wn" the Witch. As a Smoker, you can strangle the player who was tasked with Witch killing just as they are about to cr0wn her. The Witch will be startled, and the Survivor is basically a sitting duck.
 * Another good tactic as a Hunter, when possible, is to hide (standing) near the Witch, completely out of view of the Survivors (perhaps even waiting to spawn until they are close). When a Survivor is close enough, run out and slash the Witch once. She'll be instantly upset and attack the nearest Survivor. This tactic (as long as you stay hidden) does not give away your position (due to not making a sound) until the critical moment, and usually allows you to retreat momentarily and then proceed to pounce a Survivor trying to rescue the one incapacitated by the witch.
 * An Infected player can claw the Witch just as she looks up when a Survivor gets too close, sending her after them. The Witch has 1000 health in Versus, so any damage she takes from clawing is generally insignificant unless sustained for long periods of time.
 * An effective method is to have all of the Hunters surround and circle the Witch as if guarding her. Upon confrontation or encounter, the Survivors will be discouraged from advancing, knowing that the Witch is both dangerous and heavily guarded by its weaker counterparts.
 * The Jockey and Charger can quickly move a Survivor towards a Witch. In the case of the Charger, an even more destructive possibility may occur. If the Charger was killed, then the Survivor would both be freed…and be a likely target for the Witch. If the Witch was attacked before the Charger was, the Witch would both incapacitate or kill one Survivor, and free up the Charger to do much more damage.

The Survivors
This game hates lone wolves like no other. You need teammates to cover your back and pull you out of tough situations. There are a few tactics and tips you should keep in mind:

Power in Numbers:

As long as the special Infected outnumber you, chances are that they will get a combination that can leave you and your team helpless. On the other hand, if the Survivor team outnumbers the Infected team, these are the only outcomes that could possibly lead to everyone being downed.
 * A Tank, Spitter, or Jockey attacks.
 * The players that are not helpless are attacked by a horde.
 * Friendly fire, such as a poorly-thrown molotov.
 * The team fails to kill a Witch before it flees.
 * One or more Survivors falls victim to an instant incapacitation or instant kill attack (Being charged, knocked, or pulled off a ledge or out a window, etc.)

Healing:

Most healing is done when not needed; For example, if you have 30 bleed-out health (like after revival from incapacitation), do not heal. Instead, take pills or adrenaline. On easier difficulties, pills and adrenaline are not so common, while there are more first aid kits, so when out of pills or adrenaline, using a first aid kit when health is around 40 or lower is advised. On harder difficulties, as pills and adrenaline appear more common, while first aid kits are more scarce, you should wait until after your final incapacitation (when your vision becomes monochrome), because a First-Aid Kit can cure that and save you time. Try to use health kits during Crescendo Events or after a horde only if needed. If you just got up from being knocked down and you are in a finale or horde, take your Pills or Adrenaline to cover your healing time so you do not get knocked down again while healing.

Voice Chat:

Voice communication is extremely useful and most players will need to use it to ensure survival. It is not a requirement, but voice communication is a lot easier than using the message chat and it will help teammates know what is going on around them while normally offering them a quicker rescue response from special Infected and being incapacitated.

Turn On Closed or Full Captions:

If you turn either of the above on by going into options, the game will say things like "Tank growls" or "Incoming Attack". Although not necessary, this will help a lot to new players. Turning on captions can allow human players to know of incoming Special Infected even if normally out of audio range either by in-game design or volume.

Single File:

This tactic is best used in a narrow or confined space, such as hallways or tunnels. The players with the most health should cover the front and rear, while the players with the least health stay sandwiched in the middle. There should be plenty of space for two Survivors between each player, so if one is pounced/grabbed, the other players won't be knocked back, and can aid the Survivor faster. This is not a good idea to perform in Left 4 Dead 2 when a Charger has spawned, because he can easily barrel through the Survivors and cause major damage.

Moving:

One of the most important things to do on Expert Difficulty is to always keep moving forward. On Expert, the Director will almost constantly send hordes and hordes of Infected at immobile Survivors. The longer you take through a level, the more hordes and Special Infected you will need to face, so move quickly and cautiously.

One very important exception is during a horde attack. Find a spot to cover your back, crouch, and do not move! This helps to reduce team damage. If in the open, you can use a teammate's back, so that you each cover 180°.

In Versus mode, if you are not firing a weapon or shoving and you are either crouch-walking, walking or standing still, your outline will not be seen by the enemy Infected. This is very useful for sneaking up on a position where a Special Infected is likely to be hiding. Note that this will not apply to Survivors in sight of Infected players or Survivors covered in Boomer bile.

Weapon Selection:

Because of the variety of threats and the variety of weapons available, it is advisable to have different members of your team with different weapons. Some threats come from nearby and are best dispatched with a melee weapon or a shotgun, other threats are from farther away and are best hit with a sniper rifle. The environment also comes into play, as some weapons are capable of shooting through walls and others are ineffective behind walls. It is best for your team to have a mix of close- and far-quarters weapons, and ideally each team member will have something that is capable of hitting both near and far targets. If you prefer an auto-shotgun as your primary weapon, it might be advisable to take a magnum instead of a melee weapon so you can potentially rescue a fellow Survivor pulled by a Smoker. Likewise if you prefer a sniper rifle, you could find yourself in real trouble without a melee weapon if you get surrounded by a horde. A team with all shotguns or all sniper rifles is far less balanced than one with a good mix of armaments. Depending on your team dynamic and player skill, an effective mix might be one sniper rifle/melee, one assault rifle/melee, one assault rifle/2 pistol, and one shotgun/magnum (for example). The same idea goes for the throwable weapons as well. Try to have a good mix of pipebombs, bile bombs, and molotovs. Knowing when to use these items is equally important. Use the pipe bomb during horde attacks, when a survivor has been vomited on, or to clear out large open areas so the team can move faster. Use bile to slow down a tank, draw common infected away from players, or paired up with environmental hazards such as fire because the common infected will rush into the fire and be set ablaze. Use the molotovs to light the tanks on fire but be aware that it will move faster once alight and to cover a choke point. The molotov is very useful during crescendo events because if the team has to move from one area to another, such as in the mall to shut off the alarm, the person in the rear of the group can throw a molotov into a choke point behind the survivors, the fire should engulf the total area of the choke point and block any infected from coming at the survivors from behind.

Don't be afraid to vary your weapon selections either, depending on what becomes available. If you think there's a tank coming up ahead, it might be a good idea to pick up an AK47 or auto-shotgun when you come across one, even if you have to go back and pick up your laser-sighted sniper rifle when you're done.

Left 4 Dead 2 ' s Grenade Launcher is not very useful on most maps when playing in Versus mode. Its accuracy is dubious, the reloading is slow, the ammo is limited, and the potential for friendly fire damage is high. It is most effective for hitting large groups of common Infected from some distance away, and those situations don't often present themselves outside of finales. Given the potential for friendly fire in close quarters though, it's not a good primary weapon for a finale either. The grenade launcher can do a lot of damage with one shot, but when you count in the reload time it's very possible to do more damage to a single target (such as a Tank) in the same amount of time with almost any other weapon in the game. In versus mode, the Grenade Launcher is best used temporarily during a panic event or for taking out a horde during a finale, and then swapped out for something that makes less collateral damage.

Team Formation:

Some players prefer to rush and go gung-ho against the Infected, while some prefer to take the precautionary measure of taking one small step at a time. Another group of players prefer to act as the mediator between the two, constantly going back and forth to look out for players who are more audacious, and those who are more cautious. The combination of these three distinct groups of players affects the overall behavior and performance of the team. A team that has four rushers would probably finish up a map fast; but their disadvantage is that some difficulty levels cannot be rushed. A team with only rushers and cautious players might find themselves frustrated if those in front, or those behind are pounced or ambush, leading to the team's defeat, and the eventual disintegration of the team due to friction. Depending on what type of gamer you are, different combinations suit you differently. There is no correct way to play the game; so players who are competitive and quick-paced may prefer four rushers, while those who take satisfaction at teamwork and coordination would prefer a group with all three playstyles.

Squad Formation:

An effective tactic, especially in tight quarters, is to split your team into a point squad and a rearguard. The squad on point is responsible for eliminating all threats from the front while the rearguard puts the hurt on Infected flanking maneuvers. This tactic is especially effective because your rearguard and team are close enough to you that they can swipe Infected off you before they can deal damage to you.

Cornered:

Surprisingly, four Survivors crammed into one corner (or closet) works very well. Deploy two of them in a crouched position doing melee while two more stand behind them and unload their weapons, this tactic will get rid of Infected very effectively. This tactic must be abandoned with haste if a Tank, Spitter, or Charger is present. You can tell if a Tank is coming because there will be cue music, the screen will shake, and the Tank will make distinctive noises, like the other Special Infected.

Team Versus Strategy:

In Versus mode, think as the infected team would think. Like for the infected team, understanding the map and game mechanics greatly helps. Keep in mind that the enemies are human players, and use specific strategies against them.

A major strategy in Versus mode is spawning denial. That is, getting a spot into you or your teammates' line of sight or close proximity, denies your opponents spawning in that location. With good coordination via microphine, a survivor team can keep locations where enemies can spawn for good advantages in check until they get pass, forcing the opponents to either delay their attack or choose an inferior location. It is possible, although risky, to suddenly rush and get a vital location into a Survivor's line of sight before an Infected player at that location has time to react and spawn, ruining the entire ambush plan.

Tricking the enemy also works. A common trick is the Survivor suddenly stops or back away while approaching supposed ambush spots, such as a corner, a one way drop, or a Witch. This can easily trick the enemy team to spawn or attack too early, allowing the team to dispose of them more safely, or rush through while their special attack is still in cooldown.

The Infected
Coordinating Your Attacks:

This is by far the most important factor in a Left 4 Dead Versus match. If a Hunter pounces on his own, he will just get killed before he can do any real damage. If a Smoker tries to constrict a Survivor they will just get freed without any real effort, giving the Survivors about 20 seconds while you respawn or recharge and get into position to try again.

The best tactic for coordinating your attacks is to let the Boomer vomit on as many people as he can. Then, have the Hunters pounce from their hiding spots and make the Smoker pull someone away.

If the Boomer vomits on one person, then pounce or constrict the other three who haven't got Boomer bile on them! The one person will be getting attacked by Infected and will not be able to see that other Survivors have a Hunter on them or Smoker constricting them! Also, coordinate your attacks with the Tank. Wait for the Tank to spawn and let him cause havoc. Then pounce or constrict on any Survivors you see lagging behind or running off too fast. If you're a Boomer alongside a Tank, cover some people in Boomer bile and it's pretty much game over. Tanks are hard on their own, but with a horde of Infected slowing the Survivors down, they don't have much chance of escaping.

Spawning:

Most of the time during a Versus match, the Infected team will spawn one Smoker, one Boomer and two Hunters. However, sometimes it will spawn an extra Hunter as a replacement for the Smoker or the Boomer, creating a more aggressive group. This seems to happen randomly, but it appears related to which Infected die and which live. For example, if two Hunters and the Smoker live but the Boomer is killed, the Boomer player is more likely to spawn as a Hunter. Also, in very rare circumstances, there have been teams of four Hunters; this group can cause major problems even for the most experienced Survivor teams.

Do your best to learn the places you can climb to, good ambush spots, etc. Look for climbable spots that players can't reach or for strategic walls you can knock down. In general, the Boomer should spawn ahead of the Survivors so he can properly ambush while the Smoker should spawn behind to pull someone back. Hunters should be near the Smoker or the Boomer to take advantage of the chaos that they create. Obviously this is all situational as there will be times that you will want to spawn behind as a Boomer and run in.

Run Away to Respawn:

A good tactic for the Infected in Versus is to get the Director to allow you to respawn. When an Infected gets to far behind the Survivors, a message will appear giving the Infected the option of moving closer to the group. By pressing this, you will be in the respawn mode at the Survivors' location. You can now respawn where you choose with your Special Infected's ability recharged. This is a useful trick to use if you are in a bad position or want a faster recharge of your ability such as in the case of the Boomer. This method does not change your health or reset the cooldown of your special attack.

Friendly Fire
"Who's side are you on, kid?"

- Bill "I'm not a zombie, shoot the zombies!"

- Ellis "I don't know who started this shit, 'kay? But let's just stop the friendly fire right now."

- Nick

Important rule of thumb: When in doubt, hold your fire and shove.

'''Be careful EVEN when playing with Survivor Bots. There is no such thing as no friendly fire from Bots, because while their friendly fire shots don't damage you, it can easily become very annoying especially when picking off Special Infected due to screen shaking messing up your aim.'''

Friendly fire's damage will not be affected by range. Note that gunfire passing through Infected or any other surface does not count as friendly fire. But can still detonate ground placed items (such as Gas cans and Propane tanks). In all difficulties, when being friendly fired upon, the Survivors' screen will shake, they will move slower, and a damage indicator will appear on their screen. This can hinder a teammate's move and aim, and can make them mistake the enemy's position, especially when they are in panic. Even in Easy Difficulty, Survivors shouldn't attack teammates just for fun; this can cause some trouble when done at wrong moment, and will give the others a bad impression.
 * Easy - Friendly fire does not inflict damage, but friendly fire incidents will still register and disqualify players from earning the Safety First achievement.
 * Normal - Friendly fire inflicts 10% of the weapon's damage per hit to the Survivors.
 * Advanced - Friendly fire inflicts 50% of the weapon's damage per hit to the Survivors.
 * Expert - Friendly fire inflicts full damage to the Survivors. Avoid friendly fire at all costs. One shot from any shotgun will instantly incapacitate/kill a teammate!

There's a glitch if you shoot the tip of the players legs, the game will indicate that "(Player) hit (Survivor)". But would not take damage.

When a Survivor is between you and your target:
 * Hold fire and ask them to crouch. Experienced Survivors are likely to do this as long as they know of your location.
 * If they are crouched, warn them that you are firing over them, and then open fire. Otherwise, they might stand up again when you do not expect it.
 * Aim high. Dangerous weapons like the shotguns have a wider area of effect than other weapons thanks to their lack of pinpoint accuracy. Doing this will save your team from potential friendly-fire.
 * When using a shotgun, aim wide. Learn the size of the shotgun's cone of fire and aim so just the corner of your buckshot will hit the Infected. This is usually more than enough to kill a Common Infected, and can be a life saver on Expert. Do not attempt this if you feel even slightly unsure. Melee is still king when it comes to getting Infected off teammates.
 * Switch to your Pistol(s). Depending on what your primary weapon is, your pistols can be more accurate, thus lowering the risk of friendly fire. Also, the relatively low damage of the pistol means that even if you happen to shoot a teammate, minimal damage will be taken.
 * If you're slimed and your vision is obscured, look for your teammates' names, they're still visible. Shoot or push when you see motion and you don't see them.
 * In Left 4 Dead 2, melee weapons (excluding the Chainsaw) are also very useful to avoid friendly fire. They do very little damage to teammates and will not ignite explosives. When you are covered in Boomer bile, warn your teammates to keep a distance from you, find a wall or corner if possible to cover at least one side, then take out melee weapons and mow down the incoming horde.

Dangerous weapons
The following weapons have relatively large areas of effect and thus cause friendly fire havoc. On any difficulty, it is imperative that you know what you are shooting at and have the sense not to stand in front of teammates who are shooting. There are cases where entire teams have been defeated due to taking more damage from friendly fire alone than from hordes of the Infected. On Expert, minimizing friendly fire is absolutely necessary to survive as taking even a few rounds from any kind of weapon is enough to take out a huge chunk of your health and possibly incapacitate you. In the worst case, if you are seriously injured, taking even a round or two of friendly fire can kill you outright.


 * Shotguns: Do not open fire unless you are in front of your teammates. Generally, do not even try to "help" your teammates by picking off targets that are attacking them. If you must shoot, try to fire at the enemy by having them at the edge of your crosshair so that your shot will just barely hit them. This alone may be just enough to kill the enemy and save your friend. However, it's best to just switch to the Pistol, which is far more controllable than the shotgun in terms of spread.
 * Molotovs: Even on easy mode, this is the single most dangerous weapon to your teammates in the game as the fire damage is indiscriminate and has the potential to incapacitate and/or kill a teammate in seconds. It is even possible to incapacitate the entire team at the same time if the Molotov is thrown poorly. Always warn your teammates before deployment and aim it far from Survivors. The same goes for the red gas cans scattered throughout the game and are relatively common in the levels. Note that fire damage does not kill immediately, even in the case of the ordinary Infected, much less a Tank. Because of this, laying down a wall of flame that begins six inches from your own face can be worse than useless.
 * Pipe bombs: This weapon is dangerous for a different reason than the Molotov. The blast radius is small enough that it is trivial to avoid but be careful as the explosion can set off Propane tanks and Gas cans turning that trivial explosion into a seriously damage dealing problem. What is downright impossible is to avoid the horde of Infected a badly thrown Pipe bomb will attract without destroying. If needed, throw the Pipe bomb a medium to far distance away, so if you don't eliminate all of the Infected, at least they're far enough away to attack in relative safety.
 * Bile bombs: This weapon can potentially be even more dangerous than Pipe bombs. Despite the fact that it does not do damage, it summons a horde and does not eliminate it like a Pipe bomb, which can be fatal if Survivors are distracted. Use it only when during a horde, panic event, or finale wave and make sure to throw it to a good spot or somewhere far away.
 * Compressed gas cylinders: These come in two varieties, Propane tanks (white, fat and stubby, relatively common) and Oxygen tanks (green, long and slender, rare). Both of these can be thrown and detonated by gunfire to deal massive damage over a wide radius. That's the problem, in fact -- it's sometimes difficult to throw them far enough to avoid blasting yourself or your teammates. It is not possible, however to detonate these items while they are being held by teammates, should a stray round connect with them. Bear in mind that depending on what you shoot the gas cylinder with, it may not explode immediately. It will usually lose some gas before exploding unless shot with a shotgun or hunting rifle. Additionally, it should also be noted that these objects are highly vulnerable to all sorts of fire damage as well, and will prematurely detonate on their own if they are placed too close to any open flames. Despite the risks associated with these gas cylinders, they are still very useful for set-piece defense situations such as final stands or holding out against incoming hordes.
 * Grenade Launcher: The weapon can be very deadly to a team in the hands of a rookie player. The grenades do a large amount of damage even from a non-direct hit and players with little experience will tend to shoot randomly during a horde attack or at Infected who are attacking other players. While their intent may be good any rounds that explode close to fellow Survivors will cause massive damage. Fortunately and unfortunately the Grenade Launcher is rare, fortunately because that means there is less of a possibility for it to show up during a level and unfortunately since players are attracted to weapons they have not seen or used much and will therefore be more inclined to take it with them. Communicate with team members and make sure they know to use extra caution with the Grenade Launcher. Self-inflicted friendly fire damage was increased for the PC version on 9th June 2010, making the weapon even more of a hazard to the user.
 * Chainsaw: Although this weapon is classified as a melee weapon, its heavy damage can easily rip a Survivor to shreds if not careful. It is advised not to pick it up in Expert due to its high damage, the noise attracting Common Infected, and limited fuel unless the user knows what they are doing.

Survivor Deaths
Close Rescue Closet doors after you rescue a Survivor. If two people have died close together, the second Survivor will respawn after you close the door. You may need to wait half a minute or so. This is much safer than fighting to another rescue closet.

Computer Controlled Survivors
Survivor Bots, (colloquially known as "Bots") are Survivors controlled by the AI. Remember these tactics, as they can mean the difference between life or death. Bots are not really good or bad, as they have their strengths and weaknesses. It is a good idea for new players to start out in Single Player to get a good understanding of Bots and to help them play as both Survivors and Infected. Survivor Bots have specific preferences for certain types of guns, and will generally attempt to pick that type if possible. They will also prefer Tier 2 guns to Tier 1 guns, and will attempt to change weapons if in such a situation even if the Tier 2 is not their preferred type. They may also change from their preferred type to a different gun if low on ammo and a replacement preferred gun type or ammo pile is not available.

Here are advantages for both the Infected and the Survivor team. Some pros and cons to Bots are:

Pros

 * Survivor Bots are basically aimbots and can shoot Infected with notable marksmanship, always attempting to go for headshots to kill Infected faster.
 * During the credits the bots do the majority of the work for inexperienced players and can tie with a semi-experienced player.
 * They cannot trigger alarms but will refrain from attacking if they are within range of one.
 * Bots will often see Special Infected and kill them long before the player even notices.
 * They will shoot at any Special Infected except a Boomer that is too close, or a Witch that is not startled yet.
 * Bots are especially harsh on Smokers, sometimes even shooting them through part of a wall. They can quickly find and kill them faster then any other Special Infected.
 * Bots can find Special Infected, even when hiding in which a player can think of is just camoflauge. This can easily kill Hunters and Smokers trying to hide in bushes which a regular player would think has nothing inside.
 * They're almost as good at aiming while screen inhibitors arrive, such as being biled or when the storm comes in the Hard Rain chapters.
 * However, a biled bot will usually melee shove until their vision comes back or they get melee fatigue.
 * Bots will ALWAYS make sure the Infected they targeted is dead by spraying lots of ammo on them.
 * They can shoot Infected through non-clip objects where human players wouldn't spot them.
 * Bots won't hesitate to go back for a Survivor, even in a massive horde, unless they are near the rescue vehicle when it arrives.
 * Bots will not fight back if they get hit with friendly fire.
 * Bots tend to focus their attention on the Tank when one spawns, killing it extremely quickly. You should still get rid of any Special Infected trying to help them if they appear though.
 * Bots have better accuracy then human-controlled Survivors: occasionally one of the AI-controlled Survivors can get a 50% or above on their accuracy rating, in contrast to human-controlled Survivors not using scoped rifles, who usually get between 30-40% accuracy, and aim for headshots.
 * Bots are not in the least bit cowards and will fight to the end, without selfishness. This can be a problem, especially when fighting Tanks and Witches.
 * Bots can tell players where this Infected is and the direction of where it is. This allows players to find and avoid Infected. With a Laser Sight upgrade, they're even more helpful because they'll point the reticule at the Infected, allowing players to spot them easily.
 * Infected players will find it hard to split up a team composed mainly of Bots.
 * Survivor Bots will never cling to a medical kit if you are in need of it, and will give it to the Survivor who needs it the most. However it is possible for them not to give it to you, even if you are in the black-and-white mode.
 * In order to compensate for certain AI weaknesses, Left 4 Dead 2 Bots can continue to revive an incapacitated Survivor without the push-back penalty even when he/she is being attacked on the ground. Of course, if the Bot is pulled away or incapacitated, they will cease to be able to revive you.
 * Bots are never trigger-happy unlike human Survivors, saving ammo and accuracy.
 * Survivor Bots will never startle a Wandering Witch by shooting her even if it was accidental. They can still startle her by means of proximity or direct touch. However, this does not apply to the Witches sitting down.
 * Survivor Bots deal no friendly damage regardless of difficulty level. Even if they shoot straight through you or other players, it will only result in the victim (if it is a human player) to have their screens shaken, resulting in temporary accuracy loss at most. Bots never hesitate to shoot through other players if an enemy is directly behind the player.
 * However, while it is extremely rare, survivor bots can inflict friendly fire damage by shooting an Explosive Barrel and the player is caught in the blast. Bots can also cause friendly fire damage by shooting a gas can, propane tank, oxygen tank, or fireworks if they are using Explosive Ammunition if the player is near the items when they are shot. This is the only way a survivor bot can cause friendly fire damage.
 * Survivor Bots will always try as far as possible to "spread out" between other members of the team. i.e. If a human player is too far ahead, while another is too far behind, the other 2 will try to "mediate" in between.
 * On very rare occasions, a bot with a shotgun can cr0wn a Witch. This can be done when a Witch is blocking a bots' path to a safe room and cannot go around her. They will startle her first (technically taking away the cr0wning) before shooting.

Cons

 * Bots cannot see or shoot enemies through walls.
 * The only exception to this is that they will occasionally hit a Smoker through part of a wall.
 * They have no concept of bullet penetration. This means if a Common Infected runs past a sitting Witch, the bots are most likely to fire on that Infected and accidentally startle the Witch. In fragile crescendos such as the toy store in The Mall, they can set off the crescendo too early and overwhelm the team.
 * Bots will always attempt to rescue an incapacitated teammate, whether it's a bot or not, even during a finale or other situation where it would be more beneficial to leave the downed player behind, usually resulting in the bot dying. This doesn't happen in finales sometimes though.
 * This is very dangerous when a Tank has incapacitated you, as the bots will attempt to rescue you. Because of the AI Tank's attacking strategy, he will pummel anyone he can find being rescued, meaning in a few hits, you will die. This also affects human-controlled Tanks, as they will use it to their advantage and punch the rescuer.
 * Though Bots are able to shoot through human players without causing friendly fire or damage, this will still cause human player screens to shake repeatedly as if they were hit. Human players may need to move out of their line of fire or crouch if attempting to fire accurately.
 * Unlike human Survivors who know how much health and how much bullets should be expended to an Infected, those using Assault Rifles or Submachine guns usually spray their bullets on the target.
 * In Campaigns with many open areas, it's easy to have a bots short on ammo especially if infected spawns far away from bot's position.
 * Bots with melee weapons will not even attempt to move forward with their melee weapons, and most of the time use their primary weapons rather than secondaries.
 * Bots are capable of getting laser sights without letting human players know where the laser sight box is located.
 * If this happens, you should search around the nearby area for any laser sights.
 * Bots have poor methods to deal with Special Infected.
 * If a Jockey rides a player, they will try to get in melee distance and shove the Jockey off you, even though shooting from a distance is more viable despite potential friendly fire.
 * If a Charger pummels a player, they will run up to the Charger and switch to pistols, which is problematic on harder difficulties.
 * Against Spitter acid, they will not move from it unless you move far enough for them to follow you or until they start taking damage from the acid.
 * Bots cannot dead-stop Hunters and Jockeys.
 * If a Smoker constricts a player, they can either kill the Smoker from a distance or attempt to melee you out.
 * They do not dodge against the Tank's ranged attack well, usually taking heavy damage in the process.
 * They do not avoid Wandering Witches if one wanders to their location and can startle some by running past them to reach you.
 * If a Witch is startled and you are pinned (the same can apply to the Witch attacking you), you will most likely die. This is because a bot is programmed to deal with Witches at the highest priority, not saving you from the Special Infected until she dies or disappears.
 * Bots don't go ahead of human-controlled players, meaning only human players can lead groups, leaving them open to Infected attacks. This also makes Rolling Crescendos more difficult.
 * However, they will run ahead of you if they see there is a weapon or supply they want, the next safe room is ahead, or when going to the rescue vehicle.
 * The only good teamwork communication a Bot does is yelling out when an Infected is spotted. The lack of communication can work towards the Infected team's advantage.
 * Bots cannot revive dead survivors with the Defibrillator.
 * If playing alone, bots cannot lead themselves. This means if you are killed while completing a chapter, you will be forced to start from the beginning of the chapter because there are no human controlled Survivors to lead them. In Versus, this can result in the Infected team attacking the human player to end their Versus run faster. Unless the console command "sb_all_bot_game" is set to 1. Or a mods allows bots to walk on their own.
 * Generally, Bots will only pick their preferred Tier 1 and 2 weapons unless they have no choice, in which case, they will prefer Tier 2 weapons over Tier 1. However in Left 4 Dead 2 Bots will pick up any weapon other than Grenade Launcher or M60 when they are low on ammo, even when it's lower tier or not their preference. This is due to the maps in Left 4 Dead 2 which tend to have more weapons and fewer ammo piles.
 * If two ammo upgrade packs are dropped, the bots will grab both of them even if their weapon is still using an ammo upgrade from the previous pack. They may also drop them due to their weapon use programming.
 * Bots will sometimes grab another gun instead of picking up more ammunition from an ammo pile if the two are close to each other, even if the new gun is a Tier 1. This may be due to the old gun's lack of ammunition compared to the newer guns. This can be remedied if you pick up their empty gun, fill it with ammo, then switch to another gun. The Bot will generally take their old gun back this way, assuming the old weapon is better than the new gun they swapped for (and if they didn't take your gun while you were refilling their old gun).
 * Bots never use pipe bombs, bile bombs, molotovs or defibrillators. Likewise, they can never pick up gas cans (including the ones during The Atrium, The Port, and in Scavenge Mode).
 * This can be both good and bad. On the good side, this means you will not need to try to take the items before bots take it away, and you don't have to worry about if they throw it to a bad position or somewhere you don't want.
 * On the bad side, this weakens the overall firepower of the Survivors (a mixture of pipe bombs, boomer bile and molotovs are highly effective)
 * During Single Player in The Atrium or The Port, this is balanced by letting the player collect less gas cans.
 * If you are holding a Pipe bomb, Bile bomb, or Molotov and you go idle, your AI Bot will almost instantly throw it at the closest infected. If there are no infected nearby, the Bot will simply throw the grenade at the ground.
 * Bots will also refuse to pick up Chainsaws, Grenade Launchers and M60s. However, if a human player has these weapons and goes idle, the Bot is able to use these weapons and may be considered overpowered due to Bots not causing friendly fire damage. However, a Bot will immediately get rid of the these weapons for another weapon if the option is present.
 * Bots don't tend to look around carefully. This is shown especially when Common Infected are attacking them, particularly when attacking from behind, as they will usually let the Infected take free attacks behind their back. Because of this, there is 98% chance that a bot will get incapacitated when they are swarmed by a horde in Expert difficulty, even when they are in full health.
 * Bots in Left 4 Dead 2 will randomly choose between a Magnum Pistol, or normal Pistols. This can make certain situations (such as Realism Mode) more difficult where some secondary weapons may have an advantage over others. Bots are unlikely to grab melee weapons, only using them for a short duration before swapping it for pistols. However, in the game, the Survivors will always choose their preferred pistols:
 * Nick will pick up another Pistol, but if a Magnum exists, he will grab it.
 * Rochelle will pick up another Pistol, but if a Magnum exists, she will grab it.
 * Coach will pick up another Pistol if he sees a Pistol spawn.
 * Ellis will pick up another Pistol if he sees a Pistol spawn.


 * Bots handle Jockeys extremely poorly. They often have much difficulty freeing a fellow Survivor from a Jockey, especially if there are other Infected attacking. As Jockeys are almost always moving, Bots also have trouble shooting at them. Lastly, Bots don't resist Jockeys. This, when coupled with their difficulty freeing teammates from them, makes it extremely hard for a Bot to free another Bot from a Jockey, however, they can easily catch up and will either use melee to make the Jockey let go or kill it, especially when the Survivors are grouped together.
 * Bots will not attempt to cr0wn Witches, even if they have a shotgun weapon. They may also accidentally startle Witches via stray bullets by shooting Common Infected or Special Infected who are very close to her.
 * However, bots may technically (she will be startled) cr0wn a Witch if she blocks their path to a safe room with no other way around.
 * If you are incapacitated they will run to you even through fire, acid, a Witch, or a Tank.
 * Bots can be completely oblivious to items found off the main path and sometimes will ignore them altogether, even if human Survivors repeatedly point out their locations or try to push the Bots near the items. This seems to be more common in Crash Course. This affects several items, especially Health kits, but if it is an temporary healing item, players can pass it to them by using the "shove" (RIGHT CLICK for PC/ RB for XBOX 360) to give it to them.
 * Bots will not follow Infected that run off to hide. However, this can be an advantage in Versus mode.
 * Bots will not take heed to special formations you wish to create. For example, at a certain crescendo you may wish to use a specific Survivor formation at a specific spot. The Bots will follow you closely, but may leave themselves and your team more vulnerable than you wanted.
 * Bots cannot differentiate between the Hunting Rifle and the Sniper Rifle, even though the latter has a much bigger clip size. This is especially notable for Ellis if controlled by a Bot.
 * Bots also do not use the Hunting Rifle or Sniper Rifle when a zombie comes up close, instead switching to their sidearm. Seeing as how this happens very often in a typical playthrough, a Bot using these weapons doesn't kill as many zombies.
 * They will generally never pick up any First aid kits from the safe room besides their "designated" kit. For example, if you are already holding a First aid kit or Defibrillator, and the Bots on your team pick up theirs and heal, they will always leave one for you, even if you don't need it and they have a spare slot.
 * To avoid this, take a first aid kit and heal the bots before they heal themselves.
 * Alternatively, open the saferoom door and leave the saferoom. This can cause Special Infected to spawn if you idle too long, but the bot will at least grab your first aid kit.
 * Survivor Bots have worse healing strategies than human players. Or put it more accurately, the AI has a set procedure for using healing items, which in practice makes worse choices than Human players would make.
 * A Bot's decision to use its healing items is based solely on a 'health threshold'. As soon as any Survivor's health drops below this threshold, the Bot initiates its healing actions, as soon as the Survivors are not under attack by the Infected and provided the Bot has a healing item it can use.
 * Once a Bot 'decides' to perform a healing action, it is difficult (or impossible) to stop it from completing that action. Bots are relentless in their attempts to heal, and they will not stop until their target has increased in health, or until that Bot runs out of healing items.
 * Bots can't be stopped from using or passing temporary health items. Although if they pass the item to someone else, at least that person gains control of how to use that item.
 * Bots can be delayed from using First aid kits, but not stopped completely until their target improves in health somehow.
 * If the Bot is attempting to use a First aid kit on itself:
 * It can be stopped by healing the Bot yourself with your own First aid kit.
 * It can be delayed for a while by giving the Bot temporary health (which it will favor over its kit). As soon as the Bot's health dips back below the threshold though, it will again start to heal itself with its First aid kit.
 * It can be delayed for a few moments if you harm the Bot, or if the team engages more Infected.
 * If the Bot is attempting to use a First aid kit on another player:
 * It can be stopped if that player starts to heal themselves with a First aid kit, and completes that action.
 * It can be delayed for a while if that player takes temporary health for themselves. Once that player's health dips back below the threshold again, the Bot will once again attempt to heal that player with its First aid kit.
 * It can be delayed for a few moments if someone harms the Bot trying to heal, or if the player being healed brandishes a health kit (provided they have one), or if the team engages more Infected at that moment.
 * In L4D2, if player lacks any of healing items or Defibrillator, he can press W, crouch and jump. Changing position in that way will cause Bot to stop healing for very short moment, but probably enough to avoid being healed. However, player will still be slowed down due to being punched by Bot with their medkit.
 * Bots also have a specific way to heal themselves via temporary items, wasting needed supplies.
 * Falling under 60 health, Bots will immediately use their pain pills and adrenaline when if they have one. This can be a problem when there are no supplies left and the player has a fair distance to the saferoom.
 * This is also when you are at this health range and they will give it to you.
 * This poor strategy causes a lot of headaches for human-players.
 * The Bots' 'health threshold' is set much higher (health-wise) than when players might choose to heal. This leads to prematurely-used health items.
 * The Bots' "health threshold" is 40 during a normal game, but is increased to 75 when they're in a saferoom. They will still only heal other players who are under 40 while in the saferoom, but if they are at 74 themselves while inside, they will heal themselves (multiple times if they are wounded before the door is unbarred). The "saferoom threshold" also does not take into consideration for any temporary health they have. It can be subverted by opening the door and running away before the bots get a hold of any healing items, but then they tend to not go back and pick up the health kits. If they have already grabbed kits, they will ignore you and heal anyway. The "saferoom threshold" is lowered to around 50 on expert.
 * Bots may attempt to use First aid kits when players need to hurry.
 * Bots can end up having particularly poor timing on when they use their items. For example, if a Bot heals directly before a difficult crescendo, it may have wasted items that would have been much more needed following the crescendo.

Medical attention
Whenever possible, try to help fallen comrades up or cover the person helping them up. Remember, this game absolutely loves destroying lone wolves and every time your Survivor count drops you are entering a new world of hurt. When in doubt, just remember: when you're facing endless numbers of Infected, having three live people covering your back instead of two live players and one dead teammate can make all the difference. No one can survive the infection alone.

Help a friend up as soon as they fall and the area is clear. Until the area is clear, cover them. It is impossible to help someone up while Infected are attacking you or your fallen comrade. If there's a Tank and he is far away, go ahead and rescue.

It is imperative to understand that if you are facing two incapacitated survivors - one who is simply down not under attack, and one who is under attack (by a hunter pounce, smoker pull, etc.), you should help the attacked Survivor first, especially on higher difficulties.

Once you sustain damage, you can regain health with:
 * 1) First aid kit: Stabilizes your health and puts you into the green (80 or better hitpoints).
 * 2) Pain pills: Adds 50 temporary health points to your current health. In addition, having at least 40 health will allow a Survivor to run at full speed.
 * 3) Adrenaline: Adds 25 temporary health points, which decay at a slower rate, to your current health. In addition, fatigue does not act against you when shoving, you are not slowed down when hit, and you move much faster.
 * 4) Defibrillator: Commit suicide. Upon being brought back to life, you will have 50 health points that do not decay. Another perk to this method is that you can pick up the items you had when you died.
 * 5) Dying then getting "rescued", you get 50 hitpoints when your closet is opened. You with also be assigned a tier 1 weapon, and a single pistol (This means it's almost always better to kill yourself and then get resuscitated. Remember, other survivors can always use the defibrillator you dropped when you died!)

Being helped up:
 * Restores you to 30 hitpoints that decrease down to 1 hitpoint over time.
 * Only works up to 2 times unless you use a first aid kit, which resets the count. You die on the third time. It's easy to tell because your screen goes black and white and your heartbeat gets loud. Make sure to tell teammates, as it is less obvious for them, with the only cue being character dialogue.

'''Death is not permanent. How to return:'''
 * Your team mates will need to advance a certain distance beyond your body into the level.
 * You will need to wait 1 minute.
 * Your team mates then need to open the closet you will spawn in to complete the "rescue" of a "new" Survivor. It's always best to close said closet after rescue, as on some levels the same closet covers a wider than average length of the game. However, in Versus, Survivors are not allowed to return and will not respawn, apart from the Defibrillator, although this makes the team lose 25 points.
 * In Left 4 Dead 2 you can be revived with a Defibrillator and return to the game in the same spot where you were killed.
 * After completing a level, all dead team mates will respawn with 50% permanent health, and no items (health kits, pain pills, pipe bombs, etc.).