Here is the full list of all 15 Mystery Mine achievements.
Complete the 1st level
Complete the quest "Wall of Power"
Kill the Giant Bat
Defeat the Spirit of Mine
Defeat the weird Phantom
Open one of the game endings
Find all secret places in the game
Find all collectable items
Find all colletable items in the Cave
Find all collectable items in the Mine
Find all collectable items in the Deep Mine
Find all collectable items in the Underworld
Get every effect in game for once
Kill 5 different types of monsters using their weaknesses