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