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.
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
Finished mission 7
You looked at the World Tree a bit too long...
Finished mission 6
Finished mission 5
No body found during a mission
Drink 20 vials of amber
Finished mission 4
Kill an enemy who was bound by a clone
Kill a torturer in a duel
Kill more than 40 guards with throwing knives
Kill an enemy with an aerial kill
Pick pocket 15 guards
Create 30 clones
Finished mission 3
Give an orc one of your clones to eat
Let 15 clones die
Finished mission 2
Eliminate 200 enemies
Kill 20 enemies in duel
Kill an enemy with a covered kill
Finished mission 1
Unlock 20 doors
Kill two or more enemies by making a chandelier drop on them
Kill an enemy by poisoning the food
Kill 50 enemies without making noise
Finish the introduction
Extinguish 30 torches
Unlock all skills
Gather all the treasures
Unlock the Insignia of the Shadow for each mission