Beat doubles and singles tournament to get Shyguy and DK Junior.
UNLOCK YOSHI AND BABY
You can get this court if you win the Singles Tournament using Yoshi.
UNLOCK MARIO BROS.
Unlock Mario Brothers Court by winning the singles tournament with
SECOND MARIO BROS.
Unlock the 2nd Mario Bros. court by winning doubles tournament with
UNLOCK BIRDO AND YOSHI
Beat star cup doubles mode with Birdo.
UNLOCK WARIO AND LUIGI
Beat every cup with Wario doubles tournament.
MAKE BALL DISAPPEAR
In Piranha Challenge when a ball hits the net and bounces back on your side.
Run into it and it will disappear.
Note: This doesn't help you in the game, it's just cool.