Secret mode:
Choose Arcade or Arrange mode. Press Up or Select at the Difficulty Selection screen. Now at the Secret Mode screen, enter the following codes...

Secret Characters:
At the main menu, highlight arcade mode or arrange mode. Then hold left on the D-pad then press Circle. For another set of characters, instead of holding left, hold right on the D-pad and press Circle.

Another mode
Up, Up, Down, Down, Up, Up, Down, Down.

Maniac mode
Left, Left, Right, Right, Left, Left, Right, Right.

Double mode
Up, Up, Down, Down, Left, Right, Left, Right.

Mirror mode
Left, Right, Left, Right, Left, Right, Left, Right.

Thanks to Revolution readers Voodoo, nine lives, Tee, Charles and Jeffrey!