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