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