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