The Left 4 Dead Blog announces this week's mutation for Left 4 Dead 2 is Survival Versus. Here's how this is described: "The first Survivor team sets the time. The second team tries to beat it. Then the first team tries to beat the second team's time. Then the second team tries to beat the first team's time. And then the... you get the idea. Rounds keep switching until someone fails to beat the previous time." Steam News announces the new mutation is live.