The Combustible Map Pack Add-on for Gears of War 2 has 4 achievements worth 125 gamerscore.
Win a Wingman match on each of the 3 Combustible Map Pack maps
Win an Annex match on each Flashback and Combustible Map Pack map (not Custom)
Win a multiplayer match on each of the 3 Combustible Map Pack maps (any mode except Wingman)
Survive first 10 Horde waves on Combustible Map Pack maps as a team