Here is the full list of all 20 Mystika 4 : Dark Omens achievements.
Reach the high score (7 steps)
Break as many chains as you can (7 steps)
Help to restore the world (7 steps)
Trigger as many traps as possible (7 steps)
Explode as many rocks as you can (7 steps)
Become rich! (7 steps)
Cast as many spell as you can (7 steps)
Get the stars ! (7 steps)
Sell the artifacts you found (7 steps)
Dig to find more coins (7 steps)
Finish the game with Alrik !
Finish the game with Tenebria !
Defeat Elf !
Defeat Golem !
Defeat Sarel !
Defeat Selenia !
Finish a level in less than 30 seconds
Complete the first 'Spot the difference'
Find the first artifact
Reach the middle of the map