Mutations

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

- Valve

Mutations is the name for a set of modified gameplay modes, the first of which was released alongside the campaign, The Passing in Left 4 Dead 2. The Mutations are special game modes that were initially available for one week each before being retired, and replaced by a new Mutation each week following its announced on the in-game Blog Post every Friday. Periodically, a poll was conducted for players to vote for their favorite Mutation, which returned the following week as an Encore Mutation, meaning it would re-appear the next week (See below for Encore Mutations). With the download of the Cold Stream DLC you gained the ability to choose what Mutation you get to play. All mutations were made freely available for play at any time on 07/24/2012.

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:

Console Commands
To play any Mutation without it being up for that week on the PC version of Left 4 Dead 2, activate the console and type in:


 * map map filename mutation#

The map filename is any of the maps in the game, or a custom map.

Replace # with a number:

So, for example, to play Dead Center with the Ironman Mutation, type into the console:


 * map c1m1_hotel mutation8

A menu mod exists that simplifies this, as well as enabling lobbies.

Note: You cannot play multiplayer using this method.

Unrevealed Mutations
WARNING: Spoilers.

The following were found in a Steam-Group annoucement and have not been seen in a schedule as of yet. They can also be found amongst the game's script files. As they have not been announced by Valve yet, they may still be subject to changes or removal.

Encores and Developer's Choice
In 2010, after every four or five weeks, Valve would announce an encore week in which the community vote for a Mutation to be replayed. Only recent Mutations that have been played may be voted for. Alternatively, the developers would choose to replay one of their chosen Mutations for a week as a "Developer's Choice". The following encore weeks re-showcased the following Mutations:


 * Friday, May 21st (week 5) had Last Gnome on Earth return for another week.
 * Friday, June 25th (week 10) had Chainsaw Massacre reappear. On the Xbox 360, it led with 43% of the votes. However it was much more close on the PC. Chainsaw Massacre won by 1%, specifically 500 more votes, than the second most voted PC Mutation: Headshot!.
 * Friday, July 30th (week 15) had a split vote. For the PC, Versus Survival won by 6% more than Four Swordsmen. However, on the Xbox 360, Four Swordsmen won by 10% more than Versus Survival.
 * Friday, August 20th (week 18) had developers choosing Last Man On Earth to be replayed for one week on both PC and Xbox 360.
 * Friday, August 27th (week 19) had a split vote. For the PC, Gib Fest won by 5% more than Versus Survival. However, on the Xbox 360, Chainsaw Massacre won by 5% more than Gib Fest.
 * Friday, September 3rd (week 20) had developers choosing Hard Eight to be replayed for one week on both PC and Xbox 360.
 * Friday, September 10th (week 21) had developers choosing Follow The Liter to be replayed for one week on both PC and Xbox 360.
 * Friday, September 17th (week 22) had developers choosing Healthpackalypse! to be replayed for one week on both PC and Xbox 360.
 * Friday, September 24th (week 23) had developers choosing Versus Survival to be replayed for two weeks on both PC and Xbox 360, as the team will be busy 'working on their infrastructure'.
 * Friday, November 12th had Taaannnkk! reappear out of the five new Mutations, leading with a overwhelming majority vote of 51% on XBox 360 (second highest vote was Hunting Party with 17%), and 47% on PC (second highest was Healing Gnome with 17%).

Achievements & Awards

 * See Main Article: Achievements

Videos
L4D fan Rusty Woud  has a youtube channel based around gameplay videos for L4D and has also compiled video walkthroughs for many of the Mutations:

New HQ Videos:

Single/Co-op Mutations: Versus Mutations:
 * Last Man On Earth - Dead Center
 * Hunting Party - Dark Carnival
 * Gib Fest - *Expert* Hard Rain
 * Healing Gnome - Dead Center
 * Lone Gunman - Swamp Fever
 * Headshot! - The Parish
 * Versus Survival - The Parish (Bus Depot)
 * Versus Survival - Swamp Fever (Plantation)
 * Gib Fest - *Expert* Dark Carnival
 * Hard Eight - Dead Center
 * Four Swordsmen - Swamp Fever
 * Bleed Out Versus
 * Taaaaaannkk!

Older Videos:
 * Taaannnk!! - Hard Rain
 * Hunting Party - Swamp Fever
 * Lone Gunman - The Parish
 * Gib Fest - The Parish
 * Special Delivery - Dead Center
 * Nightmare - Swamp Fever (Plantation)
 * Nightmare - Hard Rain (Sugar Mill)
 * Hard Eight - The Parish
 * Bleed Out - The Passing
 * Follow the Liter - Dark Carnival (Motel)