Get All Levels
At the main menu press A, A, B, B, Up, Up.
More Mini-Games
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.
Play as Mario
Win the game in Singles.
Play as N64 characters
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.
Play as Peach
Win the game in Doubles.
Play as the Students
To unlock them at the character selection screen, defeat the students you face in the Junior, Senior, Varsity, and Traveling Leagues.
Play on Castle Court
Play Luigi's Shooting Star mini-game and win all the levels, with a score of 60 or higher on the 3rd level. You can now play on the Castle Court in both linked play and exhibition modes.
Play on Jungle Court
Play Donkey Kong's Banana Bunch mini-game and win all levels with at least a score of 60 on the third level. You can now play on the Jungle Court in linked play and exhibition modes.
Play on Tropics Court
Play Baby Mario's Target Shot mini-game and win all levels with at least a score of 60 on the third level. You can now play on the Tropics Court in both linked play and exhibition modes.
Gold and Silver rackets
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.
Star Court
Get all of the medals on the Clear Status screen.
Warehouse Court
Beat all of the Mario characters with a Mario character to get this court.