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