Left 4 Dead 2's latest mutation, Special Delivery, removes spawn timers for special infected and raises their in-game cap to 10.
Can you imagine it? The safe house is in sight; you're almost there and the effects of those hastily-consumed pain pills are quickly fading. Then you see them: two boomers, two jockeys, a spitter, a smoker and four tanks. Okay, maybe our version of the mutation sounds a bit extreme, but you get the idea.