The Onslaught Mode Add-on for Battlefield: Bad Company 2 has 8 achievements worth 120 gamerscore.
Successfully complete Valpariso in Onslaught mode on any difficulty
Successfully complete Valpariso in Onslaught mode on Hardcore difficulty
Successfully complete Isla Inocentes in Onslaught mode on any difficulty
Successfully complete Isla Inocentes in Onslaught mode on Hardcore difficulty
Successfully complete Atacama Desert in Onslaught mode on any difficulty
Successfully complete Atacama Desert in Onslaught mode on Hardcore difficulty
Successfully complete Nelson Bay in Onslaught mode on any difficulty
Successfully complete Nelson Bay in Onslaught mode on Hardcore difficulty