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 what team you are on, Infected or 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 favour.

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.

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 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 really mess up your team quickly. Shutting doors that you just came through can slow down those sneaky Infected and mean the difference between becoming incapacitated or dying, 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, many Human-controlled Infected in Versus tend to go through the level destroying all of the closed doors. That makes it easier for the Horde to rush at and attack the team of Survivors.

When the 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 use your melee attack 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.

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 and it will stall the Infected, giving you time to heal or even resupply if possible.

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 way to get to defending 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 or melee, 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 change the pace of narrow hallways, forcing Survivors to move out in the open or all get bowled down. 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.

Sadly, being on top of a car, subway cabin, or another object, is of negligible value as cover in this game due to the climbing abilities of the Infected. In fact, you'll often find yourself in a situation where you are being attacked along 360°, which in most cases is fatal. When using the shotgun, an infected circle can prove more than a little trouble, as you can't spin around shooting all near infected. Crouching can help reduce the damage recieved, as you have broader targets to shoot, along with the bullet penetration. However, gaining the high-ground while making sure your back is covered can buy you a good amount of time, due to the fact that it will take a few seconds for an Infected to climb up. Use melee or a well placed round or two to finish off a few of the horde.

Additionally, a group of Survivors all defending a high ground point, again using 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. In campaign 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.

Swamps
In Left 4 Dead 2, you will encounter swampy areas in five of the six campaigns. Swamps, naturally, will slow you down considerably, making it hard to navigate through the hordes of infected. 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 Mudmen infected easier.

Special Infected
See also: The Infected

The Survivors
Useful Precautions:
 * Listen for the heavy breathing, gagging, and burping sounds.
 * 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 cognisant 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.

When the Boomer is sighted:
 * If the Boomer is too close, it's a good idea to hit it with your melee attack, 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. It's very common 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. Use melee 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 melee him off at safe distance, the explosion will make you stumble, and this will likely cover any missed teammates in puke as well as resetting the blindness of every teammate

Helping a slimed Survivor:
 * Stay close to the stricken Survivor.
 * Help melee the horde back or shoot if the blinded Survivor stays safely crouched.
 * Help the stricken player to safely get to a corner or high ground to protect him from the horde.
 * Throw a Pipe bomb to distract the horde. (It is not recommended to throw a Bile bomb as the horde will ignore it, thus leading to the useless waste of a precious weapon.)

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. 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! Vomiting 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 normally doing large amounts of fall damage and, if high enough, will cause instant deaths. As a Boomer, don't be afraid to start clawing at Survivors if it doesn't look like you can escape.

If you explode near a car with an alarm, this will start her ! So vomit, retrait near an alarm car, and explode ! This will spawn a bonus horde !

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 AI controlled one or a player-controlled one. Even the AI waits and bides its time. As a Survivor then, your focus should be on progressing, not finding & killing the Hunter. This is especially true in Versus, where Hunter-players will often simply fly around the map with the hope of distracting & delaying inexperienced Survivors.
 * On higher AI 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
 * If the Hunter is outside pounce range, open fire. Head-shots are particularly effective.
 * Otherwise, throw a melee attack just as the Hunter starts his pounce. This will knock it back, stunning it, and you can finish it off with your choice of two additional melee attacks 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. Despite this, it is still a good idea to shove any infected, Tank and Witch notwithstanding, that are too close.
 * 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.

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. The hunting rifle is particularly effective at this, although even pistols can punch through.

The Infected
The Hunter's job is similar to that of a wolf. 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, 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 causes the Hunter to 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 melee 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 emit a scream. This allows the player to be 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).
 * ProTip : 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.
 *  ProTip : 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.

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 melee the Survivor. The Survivor will automatically be freed.
 * 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.
 * Smokers are extremely dangerous on expert, dealing 40 damage per hit when constricting a survivor. It should be imperative to save constricted team mates immediately, even if you will take damage from common infected. Left unchecked, a survivor with 100hp will be incapacitated in 3 seconds and die in 8.

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 by dragging them down from a higher part of a level as the fall will do a lot of damage, 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.
 * 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.
 * - If you manage to drag a survivor away from his team, urge a spitter to spit on the survivor you are choking.
 * - 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.

The Infected

 * Your goal is to jump on a survivor and steer them off a tall edge or into an area their team members can't get to.
 * Move around a lot amongst the survivors. You are pretty fast and can get them to shoot each other.
 * Slash with 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 if someone is low in health. Once you incap them you can move on to another target.
 * The riding my survivor mutation game is an excellent place to practice jockey tactics.
 * While riding, steer the survivor into spitter goo.
 * Take out anyone with melee first as melee weapons do huge damage.
 * You can also steer a survivor at the witch, or hide behind her with your incapped survivor. It will be very hard choice for the survivors to shoot at you.
 * Shoved off Jockey can jump again even quicker. Use that to your advantage.
 * You can also use the high buildings to feel onto survivor from above. The best way is when the roof is just above the door. Wait for all of them to leave and then quickly fell on the last one and grab him inside. Succesful attack will really slow the survivors.

The Survivors
General Tank tactics:
 * 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 immediatly 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. Its much easier to kill a tank with 4 people shooting it 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 you require 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. The propane and compressed air tanks will also knock the tank back, like 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 a Survivor. 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 the area. Good examples of crouching-only areas are ventilation grates 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.
 * 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 slows down when Infected punch 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.
 * On Expert difficulty, the Tank can incapacitate a Survivor with one punch or his rock throw. Once a Survivor becomes incapacitated, he or she 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 it is most likely you will be incapacitated.
 * Explosives deal around 750 damage to the Tank.

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 using melee and hitting it in the back. Shooting a Tank won't have the same effect as tapping it on the shoulder with your rifle butt when it's busy killing your team mate. Be aware that a Tank can turn around mid swing and smack you if you're trying to melee 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 team mates into a corner as they can't go anywhere and it is most likely they will be incapacitated.
 * If you have pills and someone else's health is in the red, give them your pills. This can prevent them from getting incapacitated. Also, if someone's health is above 41%, they can outrun the Tank. Pills provide 50% health so giving them pills will let them run faster.
 * If a team mate 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, though 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 hit them - 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.
 * 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 no one remains on the attack, 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 Tank's final chance to finish 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 a Hunter or constricted by a Smoker or you will end up freeing the Survivor and possibly saving 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. Some times 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!

The 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.
 * If she is right where you have to go, let one person go past her at a time, if she starts to get up, but you get away, wait for her to get back down and then let the next person go.
 * Potentially dangerous, but useful, it is smart to locate the Witch before leaving completely. That way, if you are retreating or need a place to hide during a crescendo event, you will know where not to go.
 * 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.
 * If you absolutely cannot get past her, your only option may be to fight 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 fire. Aiming at her back has a larger area to shoot in, while aiming at her head does more damage, but 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.
 * You can stun the witch BEFORE she is startled 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, this gives you and your team adequate time to put her down.

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 this door, then when you are safe inside, unload. This is not possible in Versus, as the safe room door cannot be closed after being opened.
 * 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.
 * Have a trust-worthy 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.

If someone else startles the Witch:
 * Make a defensive line between the Witch and the one who startled her, unload before she gets to him; 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, you can actually SAVE THEIR LIFE by shooting them and incapacitating them. The Witch will still kill them in one hit, but her attack is delayed, however, be sure to subdue the Witch before she can kill the player on the ground. Also, do not use this tactic unless the Witch is charging to attack in close proximity.
 * You can light up the Witch (best with Incendiary ammo) to change her focus onto you. Thanks to this you can make her running distance longer so your teammates can cause more damage to her. However keep in mind that she will now attack you. Don't attack her with fire after she had already killed/incapacitated someone.

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 the Tank or the 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, others will be killed by Special Infected. So stick together.
 * Don't melee the Witch -- except with the Chainsaw, and then only 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 is killed 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 crouch 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 he/she is about to crown 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 incapped by the witch.
 * An Infected player can melee 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, do not heal. Instead, take Pills or Adrenaline. On all difficulties you should wait till you are on final knock down, 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 meleeing 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 a blaze. 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 though the 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 the 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.

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 Surivivors' 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
Important rule of thumb: when in doubt hold your fire and use a melee attack.

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. In all difficulty, 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 mistaken the enemy's position, especially when they are in panic. Even in Easy, Survivors shouldn't attack teammate just for fun, this can cause some trouble when done at wrong moment, and will give the others 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 a teammate!

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 just 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: 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, fortunatly because that means there is less of a possiblity 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 change you on the margin of life or death. Bots are not really good nor bad, as have their strengths and weaknesses. It is a good idea for new players to start out in Single Player so they could get a good understanding of Bots, 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 ammunition and a replacement preferred gun type or ammo pile is not available.

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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. They're good at getting headshots too.
 * During the credits one can actually see that bots often not only kill more Common Infected and Special Infected than players do, but also have better accuracy and percentage of headshots than human players, human players have to be very experienced and active to beat them.
 * 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.
 * They're almost as good at aiming while vomited on.
 * 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.
 * Will not take it personal and fight back if they get hit with friendly fire.
 * Bots tend to focus almost all of their attention on a Tank, which can end up shredding a Tank extremely fast.
 * Bots are not in the least bit cowards and will fight to the end, without selfishness.
 * 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.
 * In order to compensate for certain AI weaknesses, Survivor Bots can continue to revive an incapacitated Survivor without the push-back penalty even when he/she is being attacked on the ground (applies only to Left 4 Dead 2 Bots). Of course, if the Bot is pulled away or incapacitated, they will cease to be able to revive you.
 * 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.
 * Survivor Bots also deal no damage to gas, fuel and propane tanks if they accidentally shoot at them.
 * 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.
 * They have no concept of bullet penetration. This means that they will accidentally shoot a boomer, startle a witch, set off a car alarm, or start a crescendo that requires the destruction of a fragile item (such as gas can crescendo in The Construction Site or the gauntlet crescendo at the windows in The Mall) when trying to kill infected near or in front of the unwanted target.
 * 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.
 * They sometimes have difficulty rescuing a pounced, pulled, or Survivors on ledges, as they may seem to walk quickly in circles around the dying victim's head.
 * Bots may take a while to save pounced/constricted/pummelled Survivors by approaching slowly, or taking their time to kill the Infected.
 * Other than against a Hunter, Bots rarely attempt to shoot at what pounced/grabbed/is riding you. They will instead try to melee shove the offender off (sometimes even when they're far away) or use a melee weapon against them. This is especially annoying when grabbed by a Smoker and lifted off the ground, as the Bots will take a long time to realise they can't reach you.
 * 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, or when the next safe room is ahead.
 * 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 generally don't do well on dodging attacks, they often evade Tanks' rock, Chargers, and Spitters' goo poorly. A Charger rush into the Survivor team with two or three bots usually means that one bot will be taken away.
 * 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 a balance for the maps in Left 4 Dead 2 tend to have more weapons and fewer ammo piles).
 * 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 in 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.
 * During Single Player in The Atrium or The Port, this is balanced by letting the player collect less Gas cans.


 * 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 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. (Due to a patch bots will now never pick up melee weapons, and will swap them to pistol if possible.)


 * 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 team mates from them, makes it extremely hard for a Bot to free another Bot from a Jockey.
 * 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 the Witch.
 * However, bots may technically (she will be startled) cr0wn a Witch if she blocks thier path to a safe room with no other way around.
 * If you are downed 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.
 * 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.
 * 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. This also means if you are carrying a Defibrillator, for example, and everyone is at a good health level, and there is one left for you, they will leave it even if they have a free slot.
 * To avoid this, take a First aid kit and heal the bots before they heal themselves.
 * Another remedy that forces a bot to take a leftover kit is to open the safe room door and exit. The bots will usually take any leftover kits through this method.
 * Survivor Bots have poorer healing strategies than human players. Or put 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.
 * 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 75-80 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 anyways. 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 team mates, 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.
 * 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, ect.)