Here is the full list of all 21 Fat Mask achievements.
Play in Solo Mode.
Play in Team Coop.
Play in Free-For-All Mode.
Complete the tutorial.
Play a 100 Free-For-All matches.
Make 10 000 points in one game.
Unlock all levels.
Claim 10 combos by yourself.
Claim 20 combos by yourself.
Claim 30 combos by yourself.
Claim 40 combos by yourself.
Steal 10 combos in one game.
Steal 20 combos in one game.
Steal 30 combos in one game.
Steal 40 combos in one game.
Create 10 monsters by yourself.
Creater 25 monsters by yourself.
Create 50 monsters by yourself.
Create 75 monsters as a team.
Fart 100 times.
Play any game mode.