You can play in a different character like the other students, Mario and Peach here is how:

Play as students
Defeat all the students you face in Junior, Senior, Varsity, and Traveling League to unlock them in the character selection screen.

Play as Mario
To unlock Mario in the character selection screen, complete the game in singles.

Play as Peach
To unlock Peach in the character selection screen, complete the game in doubles.

...I hope this helps...
...NXZ...

Mini-games:

MARIO
To unlock Mario in mini-games you must beat the game in SINGLES.

PEACH
To unlock Peach in mini-games you must beat the game in DOUBLES.

COURTS:

STAR COURT
To unlock this court, play Mario's Boo Blast mini-game, complete the levels 1 and 2, and beat the high score.

TROPICS COURT
To unlock this court, play Baby Mario's Target Shooting mini-game, complete the levels 1 and 2, and beat the high score. I think it's 60.

CASTLE COURT
To unlock this court, play Luigi's Shooting Star mini-game, complete the levels 1 and 2, and beat the high score. I think it is also 60.

JUNGLE COURT
To unlock this court, play Donkey Kong's Banana Bunch mini-game, complete the levels 1 and 2, and beat the high score. I think it is also 60.


I think the hardest court to unlock is the JUNGLE COURT.

...I hope this helps...
...NXZ...

You need patients in doing this and you need a fast thumbs or you can use your pointer and middle finger

Here is how to get the Silver and Gold Racket:

First, change your racket to the IRON RACKET (You can change your racket in TRAINING CENTER). Then go to the TRAINING COURT then go straight to the lake. You will see a kid there with cap. Talk to the kid and say his swing is bad, then after that you will try to swing and he laughs and leave. Go up where the boy is standing before.
Now you need to "Press A or B" as fast as you can in 10 seconds. If you get 100 swings you will get the SILVER RACKET and if you get 150 swings you will get the GOLD RACKET.

You can use this technique:
...You can press both A and B using your pointer and middle finger...it will make you faster...

...I hope this helps...