Here is the full list of all 13 Molecoole achievements.
Complete the first biome
Complete the green biome
Complete the red biome
Complete the black biome
Finished the game with Hearty!
Unlocked Pirate
Unlocked Fasty
Unlocked Gassy
Unlocked Blue Boi
Finished the game with the Pirate
Finished the game with Fasty
Finished the game with Gassy
Finish the game with the Blue Boi