Here on the show floor of PAX 2009, Valve is showing off one of the new campaigns from Left 4 Dead 2. It’s called Dark Carnival, and it’s a bit of a departure from some of the previous environments Valve has revealed. Unlike the first campaign Valve showed, Parish, which took place in the streets of New Orleans under broad daylight, Dark Carnival is set during nighttime and drops the game’s four survivors on a course through zombie-infested fairgrounds. We took an all-too-brief run through the campaign’s second chapter and managed to see a bit more than just the new terrain.

Dark Carnival is like an imaginative child’s worst nightmare manifested in video game form. The team of survivors must make their way through all manner of carnival-themed scenery, including striped tents, carousels, and, at one point, a giant slippery slide. But don’t take that to mean Left 4 Dead 2 has gone cheery, because this fair is every bit as creepy and twisted as the series’ other environments. In fact, it might even be more creepy, thanks in large part to one of the new “uncommon common” zombies you’ll find. At certain points, you’ll run into zombies dressed like clowns. Clowns. They’re no more powerful than the other common infected, but their squeaky clown shoes will attract more zombies the longer they stay alive. At one point, we shot one clown zombie with a shotgun, and we presumed him to be dead after he hit the ground with a missing arm. That was our mistake--a moment later this clown slowly rose back up and shambled toward us with just one arm and a gaping chunk removed from his torso. It was easily one of the more disturbing moments we’ve witnessed in either Left 4 Dead game.

This latest demo of Left 4 Dead 2 also introduced us to one of the game’s new boss zombies: the jockey. The jockey is a boss zombie who behaves very much like the hunter in the way he nimbly leaps onto you when you least expect it. But unlike the hunter, the jockey will actually take partial control over your character and pilot you toward other zombies. It’s your job to keep moving and resist his control until a teammate comes to your rescue. We also caught a look at the spitter zombie, who will spit noxious liquid onto the ground that causes you to take damage if you walk on top of it.

Thankfully, the new stuff wasn’t all on the zombie side of the fight. We also got to try out some new melee weapons. These melee weapons are a great way to test the full extent of the reworked game engine, which now allows for a lot more gibbing and severed body parts than the original Left 4 Dead. Case in point: the new katana. You’ll occasionally find yourself a ninja sword--they sell those at carnivals, right?--that has the ability to carve through zombies, sever torsos in half, and remove limbs with great ease. There’s also a crowbar that will knock the head off a zombie, and a fire axe that’s great for taking on a big group of infected at close range. We also noticed a new magnum weapon, which seemed pretty powerful, and an AK-47 that we hadn’t previously seen.

Sadly, we managed to keep hold of the controller for only one chapter of this new campaign. We were having such a good time rending zombies limb from limb with the new melee weapons that we’d love to have kept going, but it just wasn’t in the cards. You can expect to see more coverage coming your way as we get closer to Left 4 Dead 2’s November 17 release.