You can earn a star player simply by beating the Star Cup. Hold the R button as you select your character. This will make your character a Star Player.
Unlock Baby Mario and Yoshi Court
Unlock the Baby Mario and Yoshi Court by beating the Mushroom Cup/Singles Tournament using Yoshi.
Unlock Birdo and Yoshi Court
Select Birdo and enter the Tournament Mode and select select Doubles (your partner will be Yoshi) and then play till you beat the Star Cup.
Unlock Blockbuster Cup
From the Main Menu select Special Games and then Ring Tournaments.
This code will unlock the Blockbuster Cup. Have Fun!
Unlock Donkey Kong Court
Unlock the DK court by beating the Mushroom Cup/Singles Tournament with Donkey Kong.
Unlock Donkey Kong Jr.
To unlock DK Jr, you simply have to complete the Star Cup/Doubles Tournament.
Unlock Shy Guy
To Unlock Shy Guy, beat the Star Cup/Singles Tournament.
Unlock Super Mario Bros. Court
Unlock the Super Mario Bros. Court by beating the Mushroom Cup/Singles Tournament using Mario.
Unlock Wario and Waluigi Court
Use Wario and beat the Doubles Star Cup.
Unlock the Piranha Court
After beating the Piranha Challenge you can play on the Piranha Court, but only in the Piranha Challenge.