Here is the full list of all 20 Druidstone: The Secret of the Menhir Forest achievements.
Complete a non-tutorial mission without using any spells.
Complete a non-tutorial mission without any weapons equipped.
Complete a non-tutorial mission without taking any damage.
Complete The Oakshield's Demand under 90 seconds.
Complete all missions with three stars.
Defeat the Master Haunt.
Kill 9 enemies with a single action.
Complete all missions on Hard without completing any missions with other difficulty levels.
Complete all missions on any difficulty level.
Complete all main campaign missions.
Collect all Steelface's Crates.
Complete all puzzle missions.
Defeat Mad Eye.
Defeat the Necromancer.
Defeat the Ice Demon.
Defeat Oghma.
Lock an enemy into a cell.
Gain 20 power gems.
Kill both Basilisks in The Pyriform Egg.
Collect a thousand gold pieces.