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“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.

In The Sacrifice for Left 4 Dead, gamers receive the complete Sacrifice campaign with maps playable in Campaign, Versus, and Survival. There is a new style finale and plenty of places for devastating Hunter pounces.
For Left 4 Dead 2, gamers receive “The Sacrifice” campaign and L4D1’s “No Mercy” both playable with the L4D1 Survivors. Each campaign is playable in Campaign, Versus, Survival, and Scavenge modes and both feature the Left 4 Dead 2 Special Infected, items, and weapons. Yes, Zoey with a chainsaw!
Kill Bill
Have Bill sacrifice himself for the team.
As a Special Infected, incap someone who is trying to sacrifice themselves.
Supreme Sacrifice
Complete "The Sacrifice".
Chaos Generator
Have all 3 generators running at once in "The Sacrifice" finale.
Barrel Rolled
Kill a Special Infected with an exploding barrel.