Cheat Mode
Pause the game, then hold L and press C-Left(2), C-Right(2), B, A, C-Up(2), C-Down(2), Start.
Original Asteroids, Credits, and Relentless Mode
At the main menu, hold L and press C-Left, C-Right, C-Up, C-Down, A, C-Up, C-Down, C-Left, C-Right, Start.
Original Asteroids Mini-Game
Reach Zone 1, Level 15, then locate and shoot the green vector graphics asteroid that appears to unlock the classic Asteroids mini-game.