Level select:
Hold C when the Sega logo appears. While holding C sweep the D-pad in a clockwise Full-Circle starting at Up. A sound will confirm correct code entry. Press Start to display the level select screen.

Unlimited lives:
Enable the "Level select" code. Highlight the last level on the level select screen and press A + B + C + Left. Then, press A + B + C + Left again when the screen fades.

Dragon-Bio 5 ship:
Highlight the ship in the top left corner of the ship selection screen and press A + B + Start. Note: This code may only be enabled in the 1990 version of the game.

Fly same ship:
Highlight the "2 Player" option at the main menu, hold Right and press Start. Release Right after the ship selection screen is displayed. The ship in the top right should be selected for each player.

Defeat last level sub-Boss:
Collect a yellow machine gun or laser and position yourself in the lower left corner while aiming up and to the right.

Bonus level:
Locate the caves immediately following the opponents that resemble a pair of lips. Move to the top left corner to lose the current ship and restart in a level consisting of a large asteroid field.