On this page I will post each Mutation as they appear each week. Valve allows people to vote on their favorites so there's a good chance that Mutations will repeat.

Realism Versus: Just Versus mode with the Realism setting on. You can't see your human teammates but the Infected can see you and each other. Update: Votes for this mutation were so high that it became a permanent game mode.

Bleed Out: This setting works for any campaign chapter. You start off with 100 health but the bar looks as if you used pills to get there. There are no health packs only pills, adrenaline, and defibrillators. As you go through the levels, your health "bleeds out".

Follow the Liter: Scavenger mode with a catch. There's only one gas can to go after, forcing the survivors to go for it. Its a great opportunity for the Infected to lie in wait. Hint: Play as the Infected first and do your best to limit their cans and set the match to 1 for quick wins.

Last Gnome on Earth: Campaign/Versus Mode where you must carry the Gnome from "Dark Carnival" all the way to safety. But there's a twist: the Infected are attracted to whoever is holding the Gnome. Remember where you put him down! Update: Was voted to appear for a 2nd week.

Last Man on Earth: Single player campaign where you are the only survivor. There are no common infected, just Special Infected ready to take you down. Can you survive?

Chainsaw Massacre: Literally. Unlimited Gas. Campaign mode only.

Room for One: Okay this Mutation can get funny. There's only room for one survivor on the rescue vehicle, so whoever gets to it first wins! Only for Campaign Finales .