Here is the full list of all 15 One More Dungeon achievements.
Put the items in all the inventory slots
Spend 50 coins
Сomplete the game with "No margin for error" or "Curse" mutator
Die after drinking the poison
Finish the level in under 2 minutes
Buy all the mutators
Сomplete the game with "Fog" or "Broken cartridge" mutator
Squash 25 bugs
Сomplete the game
Сomplete eight levels
Kill the Ancient Necromancer
Сomplete five levels
Start the game with any mutator
Kill the Elder Flower
Сomplete the first level