Mutations

Mutations is the name for a new set of gameplay modes scheduled to appear 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 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.

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:


 * Realism Versus (Versus Mode mixed with Realism Mode, favors Infected side)
 * Chainsaw Massacre (Campaign Mode only, Survivors only have access to Chainsaws with unlimited fuel)

It is only available to those who have downloaded The Passing.

