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