Here is the full list of all 20 Chasm achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Complete the game on Hard difficulty.
Unlock all the Bestiary entries.
Complete the game as a Mortal.
Defeat a boss without getting hit.
Explore 100% of the map.
Defeat Ulak.
Complete all villager sidequests.
Break all the crates in the game.
Find all the Journal Entries in the game.
Rescue all the missing villagers.
Find all the Powerups in the game.
Defeat the Shaman.
Defeat King Trell.
Defeat 1,000 enemies.
Become the Arena champion.
Spend 5,000 gold.
Defeat the Titan.
Defeat the Bone Worm.
Defeat the Wendigo.
Defeat 100 enemies.