Invincibility
Hold [Start] on controller two at the title screen and keep it pressed until the weapon selection screen is displayed. This effect will last until the game is paused.
Nine lives
Begin game play and pass level 2. After the game ends, enter the options screen and press [Start]. A woman will appear and say "Continue Up" to confirm correct code entry. This may be repeated any time your lives have dropped below three.
Switch firing mode
Press [A] + [B] + [C] during game play.
Rotate logo
Press [A] + [C] + [[Left] or [Right]] on controller two at the logo screen. Use the D-Pad, [A], and [C] to change the size and rotation of the logo.