Enter the below passwords in the Password 18 mode to get a developer message. All underscores ("_") are meant to be blank in the password (use the arrow to skip that spot).
Enter any of the secret developer message passwords described below. After, during gameplay, press Select, then hold A+B, and press one of the following button combos for the prescribed effect.
At the title screen, opt to "Continue", then select "Password 18". These passwords correspond to the levels shown. Note that these also save the scene plan map that I had when I got these passwords.
Begin a new game and then hold down A, B, and Start simultaneously, and then press Select.