Left 4 Dead 2's first downloadable add-on has been unveiled at X10, with solid details about what the pack - titled 'The Passing' will contain.
'The Passing' sees the original Left 4 Dead posse heading down south, where naturally, they bump into the Left 4 Dead 2 survivors. Players will obviously therefore be able to play once again as Bill, Zoe, Francis and Louis.
There will be new single-player, multiplayer and co-operative gameplay incorporated into 'The Passing', with a brand new co-operative campaign with new story being a given, there will also be new Survival, Versus and Scavenge maps as well as a new co-operative challenge mode. That's a lot of new, right there.
The Fallen Survivor is also a new uncommon infected who will be added for the new episode. Apparently, the new Fallen infected class are ex-humans who thought themselves immune to the virus. Wrong! They'll drop ammo and first aid items when killed though, which is useful.
Additionally, there are plans to release a DLC campaign chapter for the first Left 4 Dead, that will explain how the survivors ended up taking a detour down to America's nether regions.
Valve are preparing the DLC for an early spring release. Gentlemen, start your chainsaws!