See Ending (Win World Series)
Go to an Exhibition game and pick your teams. When picking the stadium you want to play in, press all four C-Buttons many times. You will hear a chime if you've done it correctly. Then press The Z-Button to view the stadium. Instead of showing the stadium, you will get to see the ending of the game, just as if you have just won the world series.

  Unhittable Pitch
Place the cross hair anywhere in the strikezone except inside the yellow hitting circle. Holding the cross hair where you want it, press Z and then Left-, Right-, or Up-C to look at one of the bases. Release the Z button first, then release the C-Button, bringing you back to looking at the batter. There should now be no cross hair or hitting circle. Now throw whatever pitch you want and the computer will swing and miss or watch it go by for a strike. I suggest throwing change ups-so your pitcher doesn't get as fatigued.

  Secret Teams
Highlight 'Exhibition' on the first baseball (menu) that pops up. Now simultaneously press all four C buttons. Do this many times and you will hear a beep. Then go to the All-Star teams and there will be two new teams: Nintendo and Angel Studios. Key Nintendo executives are actual players on the Nintendo team.

Move title screen logo
At the title screen hold Z to make the baseball in the logo stop spinning. Keep holding Z and then move the joystick to make the baseball rotate however you like. It's a useless trick, but a fun one.