On the mode selection screen, select the bottom-right option and when the message appears, press Up, Up, Down, Down, Right, Left, Right, Left, A, B and Start. If done right, the debug menu should appear.
Second Player Time-Out
Normally, Player 2 cannot pause the game to alter the settings; just Player 1. However, you can enable Player 2 to do this. On Controller 1, press A and B and hold them, then reset the console. Now, if Player 2 shouts to his internal microphone for several seconds, a time-out engages.