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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.
Sacrifizzle
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.
Let’s first clear up the confusing part. Mutations are a Left 4 Dead 2 exclusive. PC and Mac players get the 5 new Mutations. Xbox 360 players only get the 5 new Mutations if they are also owners of “The Passing” DLC.

We don’t want to give away all 5 of the new Mutations, but we will give you a bit on one. Do you ever play Versus and wish you could be the Tank? Did you ever wish you could be nothing but the Tank? And when you died you spawned as the Tank? And all your friends were Tanks as well? The new Mutation Taaannnk!! is a little like that. And by a little, we mean exactly like that.
Left 4 Dead 2 will be released on the Mac Tuesday October 5th. If you already own it on the PC, then you own it on the Mac. All you need to do is install it on your Mac and start playing.

If you don’t already own it, now is a great time to pick it up. Not only do you get Left 4 Dead 2 but steam owners get all the previously released DLC for free! So you get the original 5 Campaigns and “The Passing”, “The Sacrifice” and “No Mercy.” Best of all, there is already a thriving community and excellent community created campaigns waiting for you.

Sorry Left 4 Dead owners, the Mac version is coming but we are running a little late. We hope to have it out in time to celebrate Halloween on the Mac. When released, L4D1 Mac players will receive the same great treatment. All the previous released updates and DLC for free and the ability to play an extensive library of community content. More information on the release date as it nears.