Here is the full list of all 21 The Expendables 2 Videogame achievements worth 400 gamerscore.
Complete the Campaign on Casual difficulty
Complete the Campaign on Hardcore difficulty
Interrogate the sniper
Play through an entire chapter with 4 player co-op
Complete all Challenges
Complete a mission on Hardcore without getting healed
Complete a challenge
Kill 50 enemies in a single combo
Perform all 4 fully upgraded grab moves
Blow the factory gates!
Use each weapon in the game to kill an enemy
Kill 2000 enemies using melee attack or grabs
Complete chapter 1
Complete chapter 2
Complete chapter 3
Complete chapter 4
Heal 50 times
Take out the weapons train
Upgrade 1 character completely
Upgrade all characters and signature weapons
Perform all grab moves, melee attacks and signature kills