Unlock tournaments:
     Enter  these  codes  at  the  Ring Tournament selection under the
Special games option.

A3W5KQA3C Mario Cup 
UOUFMPUOM Wario Cup  
OF9XFQOFR Peach Cup  
M1C2YQM1W Luigi Cup  
LA98JRLAR Waluigi Cup  
MM55MQMMJ Donkey Kong Cup  
ARM6JQARU Blockbuster Cup  
N24K8QN2P Bowser Cup  
J6M9PQJ6U Nintendo Power Cup  
V2UFMPUZM IGN64 Cup  
48HWOR482 MarioTennis.com Cup  


Hints:

Left-handed character:
     When selecting a character, hold L to make them left-handed.

Handicap:
     When  selecting  a  character, hold R to make them have handicaps
and be more powerful.

Get Shy Guy:
     Win the Star Cup/Singles Tournament.

Get Donkey Kong Jr.:
     Win the Star Cup/Doubles Tournament.

Get the Donkey Kong court:
     Win the Mushroom Cup/Singles Tournament with Donkey Kong.

Get the Yoshi and Baby Mario court:
     Win the Mushroom Cup/Singles Tournament with Yoshi.

Get the Mario and Luigi court:
     Win the Mushroom Cup/Singles Tournament with Mario.

Get the Mario Brothers court 2:
     Win all the Doubles Tournament Cups with Mario.

Get the Mario/Luigi Castle court:
     Win the Star Cup Doubles and Singles Tournament with Mario.

Get the Wario Brothers court:
     Win all the Doubles Tournament Cups with Wario.

Piranha Plant court:
     You  can  only  use this court in Piranha Plant Challenge. To get
it,  complete  any  court (perfect, all 50 balls) in the Piranha Plant
Challenge with any character.

Get the Wario and Waluigi court:
     Win the Doubles Star Cup with Wario.

Unlock Special Cups Tournament:
     Win  all  the Tournament Cups with every characters including Shy
Guy  and Donkey Kong Jr. to unlock the Special Cups, the hardest ones.
Press  R  when  selecting  a  character  to  access  the  Special Cups
Tournament in the menu.

Bonus difficulty level:
     To get a bonus difficulty level in exhibition mode win the planet
cup with all sixteen characters.

Get Bowser's brother:
     Play  with  wario  a  normal game and hold the ball 40 min in the
field.  If  you did it correctly then you can play with the brother of
bowser.

Get the Cyriel court:
     Play  with  any  caracter 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 correctly then you will get the cyriel court in this
court you can make your own settings.