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