While the church downstairs prepares to celebrate the Christmas season, Tripwire Interactive has been busy creating an expansion for Killing Floor that lets you kill Santa Claus, along with a special present for fans of Valve's Team Fortress 2.

Killing Floor is a cooperative multiplayer Steam game that plays a little like Valve's Left 4 Dead series, only with mutants in place of zombies. It's developed by Tripwire Interactive, a development studio located on the top floor of a church in Roswell, Georgia. A church whose attendees might have serious issues with Killing Floor's Twisted Christmas event.

Running from December 14 through January 4, the Twisted Christmas event is free to everyone that owns Killing Floor. It replaces the game's regular collection of super-powered specimens with festive holiday-themed creatures hell-bent on your annihilation. It's got evil reindeer, evil gingerbread men, and yes Virginia; there is an evil Santa Claus. Santa even gets his own level, Santa's Evil Lair, which seems a little out of character for the jolly old elf but hey, we'll play along.

Players that participate in the event will unlock a Baddest Santa as a multiplayer character. Players who participate in the event and own Team Fortress 2 will also score an extra bonus: A playable red or blue Pyro. Team Fortress 2 players will score Mr. Foster's trademark gas mask and business tie as equippable items for Pyro in that game.

Head over to the official event page for more on Killing Floor's Twisted Christmas event.