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