Thursday is the big day as the Left 4 Dead and Left 4 Dead 2 characters will finally meet up in The Passing DLC. Valve revealed some details on their Left 4 Dead blog yesterday, a handful of the downloadable content’s achievements. We know that there will be a wedding, foot lockers, and mutations. No word on what exactly a mutation is, but I would guess that it’s possible that in a versus game an infected that survives long enough can mutate. Like I said I’m just guessing, but it sounds cool, right? We will have the complete details on gameplay tomorrow. The Passing will cost you 560 Microsoft Points($7).