Valve have sent word of a fourth game mode to be included in Left 4 Dead 2, called Scavenger Mode. It's like this: "Scavenge mode challenges players to compete in round-based games of up to 8 players (Survivors vs. Infected). The Survivors must battle both the Infected and the clock as they collect gas cans to refuel a generator located in each map. Every can the Survivors pour into the generator scores their team a point and adds time to the clock." Needless to say, the infected have to stop them. Just as interesting, perhaps, is the confirmation of previously discussed Ai Director 2.0, who will have "the ability to procedurally change weather effects, world objects, and pathways in addition to tailoring the enemy population, effects, and sounds to match the players' performance."