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