The lights are on
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 will become 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 surviors to go for it. Its a great opportunity for the Infected to lie in wait.