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