Mario Superstar Baseball - Secret Characters

Baby Luigi - Complete Challenge Mode with Yoshi
Star Dash - Finish Star difficulty on all of the six mini-games
Dixie Kong - Finish challenge mode with Donkey Kong
Hammer Bro - Finish Challenge Mode with Bowser
Monty Mole - Finish Challenge Mode with Mario
Petey Piranha - Finish Challenge Mode with Wario
Toadette - Finish Challenge Mode with Peach

Unlock Koopa Castle Stadium:
Complete Challenge Mode one time.

Star Dash:
Clear Star difficulty on all six mini-games.

Toy Stadium in Challenge Mode:
In Challenge Mode, beat each of the Minigames once on any difficulty. Then purchase the Secret Map from the Item Shop for 500 coins. A Warp Pipe will appear to take you to the Toy Stadium Minigame.

Unlock Bowser for Challenge Mode:
Beat Challenge mode on Special with any character.

Unlock Coin Derby Mini Game:
Complete the Challenge Mode one time.

Unlock Grand Prix Mode:
Beat all mini games on star difficulty.

Unlock Super Star:
Complete the Item check list.