30 Extra Levels
Use FbgJ IYAX as a password.

Kid Niki
Hold A on Controller 2 at the Title Screen, until Kid Niki appears.

Preview 1st Boss
Hold Down and power on the NES. Press Up on Controller 2 after the screen turns white.

Special Game
Hold Select and power on the NES. Press Up on Controller 2 after the screen turns white.