Here is the full list of all 18 Dungeon of Zolthan achievements.
Get the dash powerup.
Defeat the first boss.
Get the higher jump powerup.
Get the double jump powerup.
Get the super dash powerup.
Get the rapid fire powerup.
Get all extra life hearts.
Defeat the first boss without getting hit.
Defeat the second boss.
Defeat the second boss without getting hit.
Defeat the third boss.
Defeat the third boss without getting hit.
Defeat Zolthan.
Defeat Zolthan without getting hit.
Complete the game with only 3 hearts.
Complete the game with 5 or less deaths.
Complete the game in 40 minutes or less.
Complete the game in 20 minutes or less.