Invalid Passwords:

The game will silently accept invalid passwords, just proceed to Start New Game after entering an invalid password.

 

Password to Judge Doom:

On the Title screen, hold A and B on Controller 2, then press Start on Controller 1. When you press Start, the character on the screen will smile and nod his head. Keep holding A and B on Controller 2 until the message "BGM + SE 00" appears on the screen.