Here is the full list of all 12 Darkest Hunters achievements.
Start mission number 1.
Defeat your first boss.
Upgrade any of your items to level 3.
Collect all notes.
Unlock your first new character.
Play in Multiplayer mode.
Find your first secret.
Open 100 chests.
Unlock all available spells.
Collect and equip all elements of one set.
Kill the Furious Lord of Darkness.
Collect all stars.