Here is the full list of all 38 Styx: Shards of Darkness achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
Unlock all achievements
Unlock all skills
Unlock Gold level for all Insignias in all missions
Finish Mission 9
Finish Mission 8
Be saved by a Life-saving Clone
Finish Mission 7
Create 50 clones
Teleport 20 times into a clone (with the skill)
Finish Mission 6
Dissolve 10 enemies (vial of acid)
Finish Mission 5
Drink 25 vials of amber
Kill all the enemies in a zone
Get out alive from 10 red alerts
Remain invisible for a total of one minute
Kill 5 guards with acid traps
Craft 30 items
Being invisible in a chest and not being caught by an enemy on a search
Finish Mission 4
Unlock your first ultimate skill
Finish Mission 3
Give of yourself to the worship of Lyssril...
Having hidden 50 times in a duct or a hideout
Finish Mission 2
Pickpocket 10 enemies
Finish Mission 1
Push 10 enemies over the edge
Collect 50 raw materials
Unlock Gold level for all Insignias in a mission
Finish a mission with the gold Insignia of Swiftness
Kill an enemy in his sleep
Finish the introduction
Finish a level without taking damage
Finish a mission with the gold Insignia of the Thief
Finish a mission with the gold Insignia of the Shadow
Finish a mission with the gold Insignia of Mercy
Complete a level without using an amber power