Here is the full list of all 20 Alone in the Dark: Illumination achievements.
HP dropped to 10% or lower, but still survived the level.
Killed 500 Creatures.
Max out a trait ability.
Complete the Mines of Lorwich Campaign.
Kill 25 creatures using Wrath of God. (Priest Only)
Complete the Mines of Lorwich Campaign in Multiplayer mode.
Complete the Cursed Railroad Campaign in Multiplayer mode.
Complete the Cursed Railroad Campaign.
Reach level 25 as the Hunter.
Complete the Tomb Beneath the Graves Campaign in MultiPlayer mode.
Reach Level 25 as the Engineer.
Complete the Tomb Beneath the Graves Campaign.
Reach level 25 as the Witch.
Kill 100 Creatures using a shotgun.
Complete every level on insane difficulty level.
Killed a Creature with a single blow.
Reach Level 25 as the Priest.
Kill 25 Creatures using Lightning Strike.
Pre-Order game OR Complete all 3 campaigns on Hard
Kill 100 Creatures using a Flamethrower.