If you have an N64 Transfer Pak and the N64 version of Mario Tennis, you can unlock some more characters and mini-games. Slap your GBC Mario Tennis in the Transfer Pak, put it in your controller, and then turn on the N64. A "Transfer" option should appear in the menu. After going to the Transfer screen and doing the Game Pak Check, choose "N64 characters," which will unlock Bowser, DK, Waluigi, Wario, and Yoshi in your GBC game. Along with the 5 characters comes their mini-games also.

In Luigi's Shooting Star mini-game, beat level 3 to unlock the Castle Court.

In Yoshi's Fruit Fantasy mini-game, beat level 3 to unlock the Tropics Court.

In DK's Banana Bunch mini-game, beat level 3 to unlock the Jungle Court.

Beat level 3 of Waluigi's Medallion Match mini-game on GBC Mario Tennis. Using the N64 Transfer Pak with N64 Mario Tennis, choose "Refresh Data" to unlock the Waluigi Court on the N64 Mario Tennis.

Beat level 3 of Wario's Treasure Box mini-game on GBC Mario Tennis. Using the N64 Transfer Pak with N64 Mario Tennis, choose "Refresh Data" to unlock the Wario Court on the N64 Mario Tennis.

Beat level 3 of Yoshi's Fruit Fantasy mini-game on GBC Mario Tennis. Using the N64 Transfer Pak with N64 Mario Tennis, choose "Refresh Data" to unlock the Yoshi Court on the N64 Mario Tennis.