It's been some time since Left 4 Dead 2's first DLC was announced. Called The Passing, the new episode would be a passing of the torch between our heroes from Left 4 Dead 1 and the squad in Left 4 Dead 2.
Valve has confirmed a spring launch of the content at Microsoft's X10 event, and with it, they've confirmed details of a brand new co-op mode called "Challenge." Sadly no details are available yet other than some new screenshots. From the looks of things we'll be killing zombies in a night club and possibly at a wedding. I bet Coach calls dibs on the wedding cake.
The first Game Add-on brings the original “Left 4 Dead” survivors down south for a meeting with the “Left 4 Dead 2” cast, while delivering new single-player, multiplayer and co-operative gameplay, exclusively for Xbox 360 and PC. Targeting an early spring release, “Left 4 Dead 2: The Passing” will include new co-operative campaign and associated narrative and new arenas for Survival, Versus and Scavenge modes, and introduce a new co-operative challenge mode.