Here is the full list of all 20 Mazes and Mages 2 achievements.
Defeat Rank 1 Boss
Defeat Rank 2 Boss
Defeat Rank 3 Boss
Defeat Rank 4 Boss
Defeat Rank 5 Boss
Defeat Rank 6 Boss
Defeat Rank 7 Boss
Defeat Rank 8 Boss
Defeat Rank 9 Boss
Defeat Rank 10 Boss
Defeat Rank 11 Boss
Defeat Rank 12 Boss
Defeat Rank 13 Boss
Defeat Rank 14 Boss
Defeat Rank 15 Boss
Defeat Rank 16 Boss
Defeat Rank 17 Boss
Defeat Rank 18 Boss
Defeat Rank 19 Boss
Defeat Rank 20 Boss