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.