Here is the full list of all 12 Slime's Revenge achievements.
Finish the tutorial
Defeat The King
Defeat Fishborg
Defeat The Golum
Defeat The Wizard
Defeat The Spectre
Collect all coins in world 1
Collect all coins in world 2
Collect all coins in world 3
Collect all coins in world 4
Collect all coins in world 5
Collect every coin in all worlds