Survival Mode

Survival Mode is a game mode which was released in the Downloadable Content from Valve Corporation; the Survival Pack. This game mode throws waves and waves of the Infected at the Survivors until they die. There is no way to really win this through surviving, but instead the goal is to survive as long as you can and set new records.

There are currently thirty-one different maps to play on in Survival Mode, thirty come almost directly from the campaign mode while a new map called The Lighthouse, which was released with the pack, but appears to be attributed with a campaign called The Last Stand.

In almost every Survival map, the map has been changed so that several areas are cut off. The only map that is not affected by this is The Atrium in Left 4 Dead 2. Such examples include boarded up doors/ladders and restrictive barriers cutting the area off from the rest of the map.

Left 4 Dead
Each survival match starts with a setup time, allowing time for you and your team to scour the map for useful items. The teams will find health kits, tier 2 weapons, pipe bombs and molotovs, pills, propane tanks, oxygen tanks, and gas cans scattered around the area. Each Survivor holds on to pills, a health kit and dual pistols at a spawn point of each map(before starting the match), right after loading the Survival game. You can take as much time as you want, as the timer at the top of the screen doesn't begin until someone hits the button that alerts the Horde. Once the button (typically in the form of whatever the chapter's Crescendo Event is in the campaign) is activated, the action gets off to a furious start and escalates from there.

Left 4 Dead 2
Survival mode gameplay in Left 4 Dead 2 is very much the same related to Left 4 Dead's survival mode.

However, there are more differences compared to Left 4 Dead. There are much more items such as Adrenaline shots, Bile bombs, varied weapons and weapon upgrades. However, the team does have to face more Infected, such as Uncommon Infected and more Special Infected.

There is also a variant of Survival Mode, a mutation called Versus Survival. It has the same format as Survival Mode but this time the Special Infected are human rather then AI-controlled.

Strategy
As always, teamwork and staying together are necessary for survival. Beyond that, survival strategies vary from map to map and from team to team. It is possible to obtain a Gold Medal achievement by staying in one area of a map, but some may find it more advantageous to move from time to time in order to get more items, ammo and avoid the Tank, and on certain maps, it can be beneficial to stay in motion and run "laps" around the map to prevent infected from catching up. Difficulty increases with time as supplies dwindle, and surviving often involves fending off multiple Special Infected and at times, multiple Tanks.

As with Versus mode (in Left 4 Dead), the melee fatigue cooldown applies.

It is always best to hole up by gathering as much resources and finding the best spot possible before setting off the Horde. For example, preparing special ammo boxes and placing Gas Cans/Propane Tanks in a secure spot can allow the team to grab it quickly in the event of a Tank attack if they do not have any Molotovs on hand.

Once the horde is alerted, the Director will send groups of Common Infected (Uncommons will appear if they can be found in that level; for example, all Hard Rain survival maps will have Worker Infected). The Director will then start spawning Tanks after 40 seconds. The times the Tanks appear are irregular, and the Director can occasionally send two Tanks at the team in conjunction with Special Infected and a horde.

No Mercy

 * The Generator Room
 * The Gas Station
 * The Hospital
 * The Rooftop

Crash Course

 * The Alleys
 * The Truck Depot

Death Toll

 * The Floodgate
 * The Church
 * The Street
 * The Boat House

Dead Air

 * The Crane
 * The Construction Site
 * The Terminal
 * The Runway

Blood Harvest

 * The Warehouse
 * The Bridge
 * The Farmhouse

The Sacrifice

 * Traincar


 * Port Finale

The Last Stand

 * The Lighthouse

Dead Center

 * Mall Atrium

The Passing

 * The Riverbank
 * The Underground
 * The Port

Dark Carnival

 * Motel
 * Stadium Gate
 * Concert

Swamp Fever

 * Gator Town
 * The Plantation

Hard Rain

 * Burger Tank
 * Sugar Mill

The Parish

 * Bus Depot
 * Bridge

The Sacrifice

 * Traincar


 * Port

No Mercy

 * The Generator Room
 * The Rooftop

Achievements
Left 4 Dead

None of the Survival Achievements are present in the Xbox 360 version of the game since it is free DLC.

Left 4 Dead 2

Tips and Tricks
These tips are general, not for specific maps.
 * Always stick together; breaking off will cause a large problem to the team and severely weaken them.
 * Try to find everything you can find in the map. Throw Gas cans and Propane tanks in a place where you won't shoot them by accident, so that you have a backup supply of "Molotovs" if you do not have any actual Molotovs.
 * Place everything you need in the area you plan to hold out in. This is useful as you do not have to run to a nearby supply area and get attacked easily.
 * Players playing with Bots will have a slight disadvantage over a team of players. While they have good accuracy, they often don't work alongside the player, especially when the Infected are swarming them. They can't use any throwables, pick up deployed weapon boxes and waste healing items. They will almost never use their healing kits if they are under attack, and have trouble rescuing players.
 * Try to find a melee weapon in the map. This is useful when you are surrounded by Infected or when killing Tanks. Most maps tend to have a couple of melee weapons scattered throughout the area.
 * A Defibrillator will be extremely useful in case the Infected manage to kill someone.
 * Have a Molotov handy to deal with the Tanks, especially when the Director sends two of them coming at you. Bile Bombs and Pipe Bombs are also useful for getting the Common Infected away from you.
 * Tanks and hordes spawn at consistent times during the first 12 minutes.
 * Tanks will consistently spawn at 0:40, 1:55, 2:55, 4:25, 5:25, 5:35, 7:05, 7:45, 8:25, 10:05, 10:45, 11:20, 11:30 and 12:50. Take note of the double Tank spawns at 5:30 and 11:30, as well as the long gap between Tanks between 2:55-4:25, 5:35-7:05, 8:25-10:05, and 11:30-12:50.
 * New hordes of common infected do not spawn from approximately 3:50-4:25, 9:00-9:35, and 12:00-12:30; this means that, during those times, the only infected that can spawn are Special Infected, making those times ideal for ammo runs, healing, or other actions that would be risky if done while infected were attacking.
 * Always try to find a spot where you have an advantage of some sort. Consider the following when choosing a place to hold out:
 * Ammunition: Is there an ammo pile or a weapon pickup nearby that you can use to replenish your ammo without having to wade through hordes of infected?
 * Supplies: Are there any other supplies nearby that you can pick up when you use the ones you're currently carrying (i.e. pills, First aid kits, etc.)?
 * Points of Entry: Where will the infected come from? Try to keep the number of entry points down to two or one, if possible, so that at least two survivors are covering each entrance. How much warning will you have when they come in that way? Will you be able to kill them before they reach you? This is the most important consideration for when you have to fight Tanks, unless you have a plan to escape when the Tank comes.
 * Escape Routes: Is there a specific route that you can take that will get you away from the infected quickly, or at least give you room to breathe and kill any major threats? Is there somewhere you can go that will confuse the Infected's AI and force them to take a longer route to reach you, buying you some time?
 * High Ground: Where do the Infected climb up? How fast do they reach you? If you fall off, get knocked off, or get dragged off, how long does it take to get back up to your teammates? How easy is it to fall off, get knocked off, or get dragged off (i.e. is there a handrail keeping you up high, or could any passing Smoker bring you down almost instantly)?
 * Line of Sight: How far away can you start killing infected? How long does it take for an infected to reach you after you can first start shooting them?  This is an especially important consideration when dealing with Tanks, because if you can see a Tank from far away, you can potentially kill it before it even reaches you.
 * Survival mode has similar mechanics to Versus mode. Jockeys and Hunters can stumble nearby players when they pin a target, and may cause them to fall off causing someone to get them back up. However, a Smoker's drag does not cause damage to players.