Here is the full list of all 37 King's Bounty: Dark Side achievements.
Complete the game with the Demoness class on Normal difficulty or higher
Defeat the Spirit of Light before 10th round
Get the achievements High Mage, Mad Courage, Reckless Fighter
Defeat the Spirit of Light in the final battle without using your Spell Book.
Complete all Engineering Department quests
Collect all the 12 Great Artifacts of Netana
Complete all Research Department quests
Get the following achievements: Greedy, Collector, Heartless, Amateur Jeweler
Accumulate at least 10,000,000 gold
Get the ogre girl for your army
Complete all Department of Experimental Weapons quests
Get the Metamorph for your army
Complete all Magic Department quests
Increase any 2 attributes of your troops to the maximum level
Gather all the companions
Inflict 300,000 magic damage during one game
Collect any complete set of items.
Take 10,000 prisoners
Open 100 chests during your travels
Train all the talents in your class tree (at least to level 1)
Collect 50 artifacts and items during one game
Get the achievements Bane of Life, Fighter, Butcher, Cool Warrior and Looking for Trouble
Receive 500,000 damage points in one game
Organize a fan club
Defeat 25 enemy armies in a row without replenishing your army
Get 15 medals (at least 1st level ones)
Destroy 100 enemy troops
Win 25 fights without using Rage skills
Win 25 fights without using the Spell Book
Deal a total of 100,000 damage points
Lose 1,000 troops
Raise your character to the maximum level
Complete all Military Department quests
Complete the game on Impossible difficulty
Increase all improvable attributes of your troops to level 3
Complete the game with the Orc class on Normal difficulty or higher
Complete the game with the Vampire class on Normal difficulty or higher