Here is the full list of all 18 DemonsTier achievements.
You died as a hero.
You bought a potion in the shop
You crafted a new weapon
get a rare chest key
Get the meta-key from the shop
you bought a master key in the shop
You killed the cave monster
You killed the spider queen
You killed the ancestral dragon
You killed the demonic spawn
You broke the illusion of thosgar
You destroyed the dreams of King Thosgar
You opened at least 100 chests
Kill the queen fly at least 10 times
Save a villager from the clutches of monsters
Finish Tier 1
Finish Tier 2
Finish Tier 3