Gaiares

Hold A+B+C+Start at the title screen to enter configuration mode. Set the sound test value to 18. Hold A on controller two and exit configuration mode. Enter the following controller actions to activate the following
cheats.

Level select - Press Start at the title screen to display the level selection screen.

Weapon select: Pause game play. Hold Up and press A to select a weapon.

Full weapons power: Pause game play. Hold Up and press B(2). Resume game play and fire the TOZ.
Note: This doesn't work with Quark Missiles (missiles your ship already has). Those still have to be powered up by capturing ships.

Legendary Power Weapon:
Fire the TOZ completely six times, then capture an enemy ship that normally awards a weapon to access the Tektite Blaster (T-Braster).

During gameplay, Pause, then press and hold... Left, A, and C, then press Start, you will be invincible for the duration of the stage you are on. (Note: There is no sound to confirm code entry.)

To gain access to the options menu, press and hold A, B and C at the title screen, and press Start.

First, access the options menu using the appropriate code.
Once in the options menu, select BGM no. 18. Press and hold the ''A'' on the SECOND controller, and exit the options menu. Once back at the title screen, press Start and you'll be able to choose the stage where you begin!