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