Those of you who pre-ordered Left 4 Dead 2 (for PC on Steam or at participating retailers) now have exclusive access to the momentous event they said would never happen. For the first time in history, two separate Valve universes collide. That's right: it's a Left 4 Dead/Team Fortress crossover! This is not fan fiction! This is not a dream sequence! The characters from Team Fortress 2 will team-up with Bill's hat from Left 4 Dead 1!