Mario Superstar Baseball

Play as Baby Luigi:
Successfully complete challenge mode as Yoshi.

Play as Dixie Kong:
Successfully complete challenge mode as Donkey Kong.

Play as Hammer Bro.:
Successfully complete challenge mode as Bowser.

Play as Monty Mole:
Successfully complete challenge mode as Mario.

Play as Petey Piranha:
Successfully complete challenge mode as Wario.

Play as Toadette:
Successfully complete challenge mode as Peach.

Play as Bowser:
Successfully complete challenge mode under the Special difficulty setting.

Koopa Castle stadium:
Successfully complete challenge mode.

Coin Derby mini game:
Successfully complete challenge mode.

Grand Prix mini-game:
Successfully complete all six mini-games under the Star difficulty setting.

Toy stadium mini-game:
Successfully complete all six mini-games, then spend 500 coins to buy the Secret Map from the shop. Use the Warp Pipe that appears to reach the Toy stadium mini-game.

Super Star:
Collect all items on the item checklist.
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Press Start, select "Check Stars," then choose a character. Look at the stars. Once all of them are filled with stars, that player will become a superstar.
Nicholas Russo.

Profiles:
Win a single player exhibition game with a player to unlock the M.V.P.'s profile unlocked at the "Exhibition Records" screen.

Hint: Easy home runs:
Go to exhibition mode and play with two players. Have player two as the pitching team, and player one on the batting team. Press A to pitch the ball. As soon as you press A, when player 2 is preparing to pitch, quickly go to player one and charge up for a charge swing. Then, hit the ball when your character is fully charged. Most of the time you will get a home run. Note: Using characters such as Wario, Donkey Kong, Bowser, and other power type characters are recommended.
austin.

Go to challenge mode and choose Yoshi as your captain. Go to Bob-omb Derby (by the Pinita) on easy mode and win. Then, go to the shop. Buy a Power Bat. Then play Peach's team first (the white and pink castle). You should hit continuous homeruns with the Shy Guys. You will later unlock Baby Luigi.
Waluigi.

Hint: Super homerun:
When batting, hold R to do a Star Swing. Hit the ball in the sweet spot to achieve a "super homerun". This super homerun cannot be blocked or caught, and will always go out of the park. When executed in an Exhibition game, it will use all five of your Team Stars. Use "Free Batting" under the "Practice" menu to try it, or for a demonstration.
Jair Ross.

Hint: Father and Son homeruns:
Bowser must hit a homerun and Baby Bowser must to hit a homerun immediately afterwards. To do this you must not have bought either of their specials (the bullets). Start a game (Yoshi recommended) and use a star with Bowser. If it does not foul you should automatically get a homerun. Repeat this with Baby Bowser. As long as you do not have the specials it result in a homerun almost every time.
Jonathan.

Hint: Easy challenge mode:
You will complete challenge mode quickly if you use Peach's or Yoshi's team. You will then unlock Baby Luigi or Toadette.
Waluigi.

Hint: Nice pitch:
With Mario pitching, press A to make him start his wind-up. When he reaches the top of his jump, press A again to make him pitch a "Nice". Note: This may require a few attempts.
Rene Campos.

Hold A to pitch. Count to four and release A. You will throw a "Nice" pitch.
Andrew Finelli.

To get a "Nice" pitch every time, look for a flashing light under the character when charging. When releasing at this point, he or she should always throw nice pitch, though may require some practice. Note: Waluigi is the best pitcher.
Tallandnerdy.