Given the extreme pace of Survival Mode, the number of zombies killed in a single round often outnumbers an entire campaign. Even optimizing towards using pistols to eliminate common hordes, ammunition usually becomes an issue at some point. As ammo piles provide a unique infinite resupply for players, they tend to be in relatively less defensible positions in the Survival arenas.

The Hospital Elevator, for example, might seem like an easy Crescendo Event to conquer. Hit the elevator button and holdout until the doors open for a quick escape. In Survival Mode, however, the area begins locked down. Areas open as the hordes come in, breaking down the doors to reach the survivors. In each room there are additional caches of vital pills, pipes, and Molotovs. By moving from location to location, using up the plentiful supplies as needed, a team can maximize their time in a game where the elevator never arrives to offer escape. In other maps, items may be less plentiful and require careful planning on their usage. Managing one's inventory and resources works hand-in-hand with teamwork in Survival Mode.

How furious is it? Consider this: In all of the play testing that the Valve designers have done while creating this mode, none of them have ever survived past the 10 minute mark. We're told the company best so far was about nine minutes, with a team of elite players battling like crazy to keep one another alive. Our experience at Valve averaged around three or four minutes a round, but they're like the fastest three or four minutes of your life.

What makes it so challenging is that the Survival mode doesn't waste time building up. After the initial wave of zombies you'll start getting hit by waves of special zombies; these are the hunters, smokers, boomers, and tanks. You'll get multiples of them at a time; I often saw two or three hunters or smokers leaping around the battle while the mindless horde minions were everywhere. In one battle, we had the tank, a boomer, a couple of smokers, and a hunter hitting us at the same time. We're told it's even possible to get two tanks at the same time, a prospect that seems both ludicrously unfair and hilarious at the same time.

As soon as your group is wiped out, you get the match results and then the entire thing resets. Basically, once you start playing you can do round after round easily, which eats up the time. Survival mode is playable on 16 levels, 15 of which are taken and modified from the existing four campaigns. We played in Dead Air's airport terminal, Blood Harvest's farm house level, and No Mercy's hospital level. There is one entirely brand-new level in the DLC called Lighthouse which the designers say may be the toughest level of them all.

Lighthouse is exactly that; a lighthouse atop a seaside cliff. You also get a sense of what you're in for when you realize that you start with a ridiculous amount of stuff at your disposal. There are about a dozen gasoline containers and propane tanks, as well as plenty of Molotov Cocktails and pipe bombs. It's like that age-old first-person shooter tradition of giving you plenty of ammo and health before encountering a major boss. What makes Lighthouse so dangerous is that it's a pretty open level; there aren't a lot of places to hide, and those places are pretty porous once the zombies start knocking holes in walls. Even the lighthouse tower itself is dangerous; while it's scenic and gives you a height advantage, you're exposed to any smoker who can grab you and drag you off the room with its tongue. You're in a dire position if you're on the ground and the rest of your teammates are still in the tower.