Secret Message: Only appears in the US version. At the title screen, hold A or B or both then press Start. A staff screen will appear.
Credits screen: Play exactly 10 games, no matter if you win or lose. It can even be the games played in WATCH mode by the computer itself. After the 10th game is over and the game returns to the title screen, a credits screen will appear before the team names demonstration.
Debug monitor: any time during the game, hold Up + Down on controller 1, then press Right, Left, Down, Up on controller 2.
A set of numbers will appear at the top-right corner of the screen. The upper four represents the address, and the bottom two are data value at the selected address. Press B on controller 2 to enable address and data edit: change any digit using the D-Pad buttons on controller 2, or press the previous combination to save your changes. You can watch any ROM or RAM data and change any RAM data.