Mario Tennis

At the main menu press A, A, B, B, Up, Up.

Equip the iron racket. Go to the training court. Go to the lake and talk to the kid praticing his swing. Talk to him and tell him you hate his swing. After he shows you his swing press a 100 times for the silver and 150 times for the gold racket.

Unlock the Nintendo 64 characters, then check the mini-game screen. More entries should be available. To unlock even more mini-games, win the Junior, Senior, Varsity, and Traveling Leagues in Singles and Doubles.

Win the game in Singles.

This will allow you to play as Bowser, Waluigi, Wario, and Yoshi. Use the Transfer Pak with the Nintendo 64 version of Mario Tennis. Select "Transfer" at the main menu, then select "Game Pak Check". Select the "Transfer N64 Characters" icon.