Here is the full list of all 43 Foreign Legion: Multi Massacre achievements.
Snipe 250 prairydogs
Make 250 fueltanks explode
Make 1000 enemy headshots
Make 100 fueltanks explode
Shoot 69 peacedoves
Snipe 100 prairydogs
Make 25 fueltanks explode
Make 250 enemy headshots
Blow up 250 dolphins
Start the Generator 100 times
Kill 1000 zombies
Shoot 30 peacedoves
Make 50 enemy headshots
Blow up 100
Pop 250 pumpkins
Shoot 7 peacedoves
Blow up 25 dolphins
Honk your clowns nose 500 times.
Start the Generator 50 times
Snipe 25 prairydogs
Kill 250 zombies
Break 250 wooden boards
Start the Generator 25 times
Shoot off 250 zombie limbs
Pop 100 pumpkins
Break 250 tombstones
Finish a game in EXTREME
Break 100 tombstones
Break 100 wooden boards
Kill 250 players
Wear the BunnyEars and jump 500 times.
Kill 100 players
Kill 25 players
Break 25 tombstones
Pop 25 pumpkins
Host a 3 player game
Shoot off 100 zombie limbs
Kill the ghost on time
Kill 25 zombies
Shoot off 25 zombie limbs
Host a 4 player game
Win a domination game.
Break 25 wooden boards