On the Password entry screen, enter the letter "Q" in every space (16 total). After entering the last letter, the message "Invalid Password" will appear. Press the B Button to back out one screen to the Title screen, then enter Options to find the Debug mode option at the top.
Debug Mode options: Start Map: Choose any Level from 1 through 25.
God Mode: You can be invincible. Default is Off.
Weapons: Gives you all the weapons in the game. Default is Off.
Target: Turn it off so enemies will not see you. Default is On.