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