Unlock Metal Mario
From the main menu, select Special Games, and then Ring Tournaments. At that screen type in 'MMAR10PCN'. If done correctly you will hear a clanking sound.
Trick Shots
This cheat works only if your opponent is on the baseline. If your opponent is on the base line and he/she just hit it charge up a trick shot by pressing B and A(B 1st then A). Then when he/she is close to the net press A and B(A 1st then B).
Birdo-Yoshi Court
This is really simple. Just win the star cup doubles tournament with Birdo. (Yoshi will be your doubles partner)
Secret of the Smash
You probably know that pressing A+B together on a star, you can create a powerful "Smash Technique". But, there is yet an even more powerful way to smash this nearly unblockable technique. Like before, go directly under an available star. You may also go up to the net. When the ball comes, hold up, and press A+B twice. If you want, CHARGE UP (holding up while pressing A+B repeatedly) the shot before hitting.
Get the Cyriel court
Play with any character on the grass court then hold the ball 1 hour in the game with out make a point (this most be play in one player) if you do this correctly then you will get the cyriel court in this court you can make your own settings.
Bonus difficulty level
To get a bonus difficulty level in exhibition mode win the planet cup with all sixteen characters.
Nintendo Ring tournaments
Select the "Special Games" option at the main menu, then choose the "Ring Tournament" selection. Enter "A3W5KQA3C" as a code at the code entry screen to play a tournament for the Mario Cup. Another code will be displayed after completing the tournament. The new code is not actually a code for the game, but is for ranking you with other players at Nintendo's Mario Tennis web site.
Enter "J6M9PQJ6U" as a code to play as Donkey Kong Jr. vs. Bowser in another contest.
Mario/Luigi Castle court
Win the Star Cup Doubles and Singles Tournament with Mario.
Piranha Plant court
Note: This court only works in Piranha Plant Challenge. Complete any court (perfect, all 50 balls) in the Piranha Plant Challenge with any character.
Wario Brothers court
Win all the Doubles Tournament Cups with Wario.
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