You'll need a second controller for this one. Start a new game and then pause. While the game's paused, hold Down/Left on Controller 2, then press Start, then press B. You'll see the word 'Pass' show up, meaning the code's worked. From there, you've got a wide array of commands at your disposal using both controllers, as follows...
A - Disable 'Pause' text (clean pause, use for taking screenshots).
B - Toggle between 'No Hit' (invincibility), 'Free Play' (infinite lives), or switch both off.
C - Skip to the next stage.
A - Give yourself $99999999 (!?!).
B - Disable 'Pass' text (not sure what this does).
C - Destroy all Enemy Generators, skipping to the boss.
Arcade Fantasy Zone Music
The more observant among you might notice that the sound test contains not only the music from the actual game, but also the entire soundtrack from the original Fantasy Zone arcade game. Now, why's that? It's because you can actually have this music play instead of the default music. It'll even replace the Shop and Boss music, but for some reason, Ya-Da-Yo (Final Boss music) and Victory Way (ending) from the arcade game were left out. I was sent this cheat in by a man who called himself DeGgozZ back when people read the pitiful guide I wrote for the game on GameFAQs, but because I lost my account, I never updated it. Sorry it took so long...
Anyway, on the title screen, hold A+B+C and then press and hold Start until the game starts to replace the music.
Did this really deserve its own page?