Homerun
In game { two player mode only,}when a player that is on the allstar team is up to bat,press start, then press B,Y,B,Y select. Now any ball you hit{that is a fair ball,} will be a homerun!
Slow Mode
Pause the game at the batting screen. Then, press Left, A, Right, Down and Y to slow the opposing team to a crawl. This works whether you are batting or fielding. The effects last for the remainder of the inning.
Random Pitches
Pause the game at the batting screen. Then, press L, Y, A and Right while batting to make the opposing team's pitches become random. For example, if the opposing picture tries to throw a fastball, it may become a curve. The effects last for the remainder of the inning.
Hidden Teams
After completing a full season, press A, B, X, Y, Up, Down and Select on the Title screen to access hidden teams. The longer the season completed, the more teams will be available.
Max Ability
Pause the game at the batting screen. Then, press A, Right, Down, Left, A and Down to maximize your team's abilities in all areas. This works whether you are batting or fielding. The effects last for the remainder of the inning.