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