Here is the full list of all 20 Dark Gates achievements.
Upgrade a hero
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Save Game
Party is dead
Successfully negotiate with a monster
Successfully bribe a monster
Kill one hero
Land a maximum damage hit
Land a critical hit
Save a party layout for next time
Destory Dark Gates on easy difficulty
Destory Dark Gates on normal difficulty
Destory Dark Gates on hard difficulty
All heroes are dead, game over
Kill the Unnamed
Reset the game
It's alive!
We want no trouble
Scare a monster
Gather 5000 in gold