Here is the full list of all 26 8 achievements.
Beat the puzzle and defeat miniboss 2
Beat dungeon 2
Beat dungeon 1
Defeat miniboss 1
Beat the puzzle and defeat miniboss 3
Beat the puzzle and defeat miniboss 4
Defeat miniboss 5
Find and defeat miniboss 6
Beat the puzzle and defeat miniboss 7
Beat the puzzle and defeat miniboss 8
Beat the puzzle and defeat miniboss 9
Defeat miniboss 10 at the colosseum
Beat the puzzle and defeat miniboss 11
Beat the puzzle and defeat miniboss 12
Beat the puzzle and defeat miniboss 13
Defeat miniboss 14
Beat dungeon 3
Beat dungeon 4
Beat dungeon 5
Beat dungeon 6
Beat dungeon 7
Beat dungeon 8
Beat dungeon 9
Beat dungeon 10
Beat dungeon 11
Beat the puzzle and enter the tower