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