At the main menu, enter the last option. On the new menu screen, select the last option and press Select. If done right, you should enter the secret option menu and watch the credits.
Self-Test
Note that this cannot be done without a Famicom controller that allows you to press all four D-Pad buttons at the same time. Press all four D-Pad buttons simultaneously on Controller 2, then reset the console. The game will run through a PRG ROM, CHR ROM, and a save-RAM test.
Skip to round six
At the "PLAYBALL!!" screen, hold Left + Select. When the game starts, a sound will confirm correct code entry. Now you'll start from the sixth round.