Here is the full list of all 20 One More Dungeon 2 achievements.
Die for the first time
Complete the first level of the dungeon
Defeat the First Boss
Defeat the Second Boss
Defeat the Third Boss
Defeat the Fourth Boss
Destroy the Creature
Change character class
Clear all skill statues
Collect 500 gold while exploring the dungeon
Reach the tenth character level
Get five curses
Donate 50 gold
Summon and destroy the Demon
Find and return the shell
Destroy 100 monsters in one run of the dungeon
Destroy the King Beetle
Overthrow the Snail King
Clear all class statues
Find the Leprechaun