The Sacrifice is a three-map campaign with a story that links the two games and takes some of the mystery out of the events portrayed in Valve’s previous L4D2 DLC pack, The Passing.

“The Sacrifice” is the prequel to “The Passing,” and takes place from the Left 4D Survivors’ perspective as they make their way South. We know Bill dies in “The Passing” but how and why? You can read the comic to find out the official version of events or this October 5th you can play the game to choose your own ending.

The Sacrifice is available for L4D and L4D2, and as an added bonus, the new DLC will give L4D players the new machineguns and melee weapons released in The Passing. And L4D2 owners will receive one of the original game’s most popular campaigns, No Mercy.

The main draw of The Passing will be the crossover that’ll occur between the survivors from the first Left 4 Dead and the new survivors in Left 4 Dead 2. But on top of that, The Passing also brings a number of other new items and gameplay modes with it as well. One is the new “Mutations” system, which Valve describes as a “series of weekly game mode events” that include modes like “Versus Reality” and “Chainsaw Massacre” — the latter giving all players chainsaws with infinite gasoline. Valve has 20 different Mutation modes planned.

Other new features include a new co-operative challenge mode, support for infected bots in Versus mode, a new golf club melee weapon, new M-60 machine gun, and a new “uncommon common” infected class…that has a little something to do with the L4D1/L4D2 crossover. Read here for some more spoilerish details on how that’ll work.

Set in the zombie apocalypse, Left 4 Dead 2 (L4D2) is the highly anticipated sequel to the award-winning Left 4 Dead, the #1 co-op game of 2008.

This co-operative action horror FPS takes you and your friends through the cities, swamps and cemeteries of the Deep South, from Savannah to New Orleans across five expansive campaigns.

You’ll play as one of four new survivors armed with a wide and devastating array of classic and upgraded weapons. In addition to firearms, you’ll also get a chance to take out some aggression on infected with a variety of carnage-creating melee weapons, from chainsaws to axes and even the deadly frying pan.

You’ll be putting these weapons to the test against (or playing as in Versus) three horrific and formidable new Special Infected. You’ll also encounter five new “uncommon” common infected, including the terrifying Mudmen.

Helping to take L4D’s frantic, action-packed gameplay to the next level is AI Director 2.0. This improved Director has the ability to procedurally change the weather you’ll fight through and the pathways you’ll take, in addition to tailoring the enemy population, effects, and sounds to match your performance. L4D2 promises a satisfying and uniquely challenging experience every time the game is played, custom-fitted to your style of play.

Featuring new Survivors, boss zombies, weapons, and items, Left 4 Dead 2 offers a much larger game than the original with more co-operative campaigns, more Versus campaigns, and maps for Survival mode available at launch.