Extra levels
Enter FbgJ IYAX or GdBM IABg as a password to play additional levels.
Kid Niki
Hold A on controller two at title screen, until Kid Niki appears.
Sound test
Hold A + B on controller two at the title screen and press Reset. Press A or B to select a sound and Up, Down, Left, or Right to play them.
Preview first Boss
Hold Down and power on the NES. Press Up on controller two after the screen turns white.
Special game
Hold Select and power on the NES. Press Up on controller two after the screen turns white.
Suicide
Press Select during game play to end the current game if you become stuck.