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