Here is the full list of all 33 Styx: Master of Shadows achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
Unlock all skills
Gather all the treasures
Unlock the Insignia of the Shadow for each mission
Do not use any item during a mission
Manage to disable three guards, or more, inside a clone's smoke bomb
Eliminate a guard with a booby trapped clone
Kill more than 40 guards with throwing knives
Finished mission 7
Pick pocket 15 guards
Drink 20 vials of amber
Finished mission 6
Let 15 clones die
Kill 20 enemies in duel
Create 30 clones
Unlock 20 doors
Kill an enemy who was bound by a clone
You looked at the World Tree a bit too long...
Kill an enemy by poisoning the food
Eliminate 200 enemies
Finished mission 5
Finished mission 4
Kill a torturer in a duel
Kill an enemy with a covered kill
Finished mission 3
Give an orc one of your clones to eat
Finished mission 2
Kill 50 enemies without making noise
Kill an enemy with an aerial kill
Finished mission 1
Extinguish 30 torches
Kill two or more enemies by making a chandelier drop on them
Finish the introduction
No body found during a mission