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