Mutations

"Each week one new Mutation is featured and the previous Mutation retired."

- Valve

Mutations is the name for a new set of gameplay modes that was released alongside the new campaign, The Passing in Left 4 Dead 2. The Mutations are special game modes that run for one week before it is retired, and replaced by a new Mutation each week as they become announced on the in-game Blog Post every Thursday. Presumably after all the Mutations have been revealed, a poll will be conducted once a month for players to vote for their favorite Mutation, which will return the following week. It is only available to those who have downloaded The Passing.

Revealed Mutations
There are over 20 different Mutations planned, and playable on all Left 4 Dead 2 Campaigns.

So far, the following have been revealed on Valve's blog in the scheduled order along with their taglines:

Unrevealed Mutations
The following were found in a Steam-Group annoucement and have not been seen in a schedule as of yet. As they have not been announced by Valve yet, they may still be subject to changes or removal.

There are four more Mutations, but nothing more is known about them. The mode that they will be used in, however, has been confirmed. There are:


 * 2 More Mutations for Campaign Mode.
 * 1 More Mutation for Versus Mode.
 * 1 More Mutation for Scavenge Mode.

Bleed Out

 * A good tactic for this is if you all have headsets and you like teamwork, because every one will have their own part in this, is to have all four Survivors bunched throughout the campaign. The front Survivor is the one on point, as they will be the first into a room to look for Special Infected. If the Survivor is pinned the other three will be close by, shooting the Infected. The Survivor on point will most likely be very damaged because of the temporary health, so they will use their Pills (or someone else's, if players want to keep that Survivor on point duty, the lineup can be changed along the way). But don't forget, the other Survivors' health will be ticking down, too, so the back Survivor will look behind them for Pills and adrenaline. If found, that Survivor will inform the others. The middle two Survivors will have the easiest job, killing all of the stray Common Infected, or Special Infected. If everyone stays together, if one gets pinned the others can save them. This may be a very common tactic for most if not all game modes, but may be effective for this Mutation in particular.
 * Alternatively, since health decreases based on the amount of time you spend up, the logical decision is to rush wherever possible so that no time is wasted exploring every nook and cranny. Shotguns and melee weapons are the best way to achieve this tactic. Any nearby clusters of Common Infected can be dealt with on the move in order to stop them from surrounding you, and any Infected chasing the team can be quickly melee'd away to gain a large amount of distance between you and them. If every Survivor adheres to this tactic, there will be relatively few Special Infected each stage depending on difficulty and Director's mood, the team will be close together, and if someone is grabbed then the other teammates should be close by to save them. This can be achieved relatively easily with as few as two Survivors as long as they both make sure to stick together, keep their ears open for Special Infected growls, and protect each other. Do not worry about ammunition, as there should be plenty of weapon spawns along the way. This strategy is particularly effective during Expert difficulty, as this difficulty carries an even greater sense of urgency, since Infected do such significant amounts of damage that you cannot afford to have numerous hits taken. Finales should be treated as normal, but do not be afraid to constantly be on the move in order to stop yourself getting trapped in a corner by multiple hard-hitting Common Infected.