Oh, sweet! Killing Floor is free to play this weekend! For those of you who don't know, Killing Floor is a PC horror themed FPS that offers online co-op for up to six players. We reviewed it way back in 2009, and we really enjoyed the title, giving it a 4.5/5. Not only is the game free to play, there's also a "Twisted Christmas" event going on. That's right, you can blast mutant reindeer and gruesome gingerbread men into tiny little bite-sized pieces. The "Twisted Christmas" event also includes new weapons, new achievements, and a new map. All of the details are right here. Check out the following video for more information.