The Sacrifice is a DLC campaign for Left 4 Dead[Clarify] and a built-in campaign for Left 4 Dead 2. While originally slated for release only as a L4D campaign, The Sacrifice was delayed over five months and eventually released for both games.
The Left 4 Dead 2 version of the campaign includes all of the new weapons and special infected featured in the game. Additionally, the original Left 4 Dead characters models were ported over for the campaign, and new dialogue was recorded for them.
- func_nav_avoidance_obstacle (was used in L4D1, like Dead Air 2)