At any mode except the Pennant mode, when you get to the Stadium select screen, hold Select and press Run to unlock the hidden Base Island stadium.
At the mode select screen, chose either an "Open", "Watch" or "All Stars" game. Then at the team selection screen, press the following buttons to unlock the hidden teams:
Effect Code Gsan Team Hold Run and press Button 1. Hudson Team Hold Select and press Button 1.
Play As The Same Team
At any mode except the Pennant mode, hold II + Select and move the directional pad to be able to choose the same team as the opponent.
Skip To The Japan Series
Enter the Pennant Mode and choose New Game. Pick your team and then the number of games, but before going on any further, hold Run and press Select to reset the game. Now, enter the Pennant Mode again, pick your team and hold Run and press Select to reset the game again. Finally, choose the Pennant Mode again and you'll automatically be at the Japan Series.
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