Mario Power Tennis cheats and cheat codes for Gamecube

Event mode: Hold Z, then press Start at the title screen. 

Ace mode: Beat the Planet Cup tournaments in singles or doubles mode. 
Balloon Panic mini-game: Beat the Flower Cup tournaments in singles mode. 
Bowser court: Win 1st place the Special Cup Fire tournament in singles mode. 
Characters with star: Beat all three Normal Cup tournaments with a character
Coin Collectors mini-game: Beat the Mushroom Cup tournaments in singles mode. 
Fly Guy: Earn the Mushroom, Flower, and Star Cup in singles mode. 
Mario Bros. court: Beat the Special Cup Lightning tournament in doubles mode. 
Mecha Bowser Mayhem mini-game: Beat the Mushroom Cup tournaments in singles mode. 
Moonlight Cup: Beat all the Rainbow Cup tournaments. 
Paratroopa: Beat all 3 Normal Cup tournaments in doubles mode. 
Petey Piranha: Earn the Special Cup Fire and Lightning tournaments in doubles. 
Shy Guy: Win 1st place on all three Normal Cup tournaments in singles mode. 
Star Cup: Beat all 3 Normal Cup tournaments. 
Unlimited Balloon Panic Challenge: Finish Ultra-Hyper Panic. 
Unlimited Coin Collectors Challenge: Finish the Gold Rush Challenge. 
Unlimited Gooper Blooper Volley Challenge: Finish Master Blooper. 
Unlimited Terror Tennis Challenge: Finish Phrantic Phantoms. 
Unlimited Tic-Tac-Glow Challenge: Finish the Dazzle Shine Challenge.
Wriggler: Earn the Special Cup Fire and Lightning tournaments in singles mode.
                
More options in Special court:
Play a special court in the Special Cup

Change Yoshi's defensive power shot color:
Beat the Flower Cup tournaments in doubles mode. 

Skip credits:
Hold Start + A.

Taunts:
Hit A or B while your opponent hits the ball. 

Random character or court:
Hit X at the court or character selection screen. 

Terror Tennis unlockables:
Reach the indicated amount of point on the indicated level within the time limit:
Pesky Poltergeists: 50 points in the "Goofy Ghosts" level
Phrantic Phantoms: 150 points in the "Pesky Poltergeists" level

Artist on the Court unlockables: 
Complete the indicated paintings within time limit.
Yoshi's painting: Complete Bowers and Bowser Jr.'s painting
Luigi Painting: Complete Mario's painting
Diddy Kong's painting: Complete Luigi's painting
Bowser and Bower Jr.'s painting: Complete Diddy Kong's painting

Balloon Panic unlockables:
Super Panic level: Finish the Panic level. 
Ultra-Hyper Panic level: Finish the Super Panic level. 

Chain-Chomp Challenge unlockables: 
Famished Chomp level: Finish Hungry Chomp level with the highest score. 
Hungry Chomp level: Finish Perkish Chomp level with the highest score. 

Coin Collectors unlockables:
Coin Challenge level: Finish the Gold Rush level. 
Gold Rush level: Finish the Jackpot level. 
Jackpot level: Finish the Fever level. 

Gooper Blooper unlockables:
Master Blooper: Finish the Rival Blooper level. 
Rival Blooper: Finish the Buddy Blooper level. 

Mecha-Bowser Mayhem unlockables: 
Iron Frame level: Finish the Aluminium Frame level. 
Titanium Frame level: Finish the Iron Frame level. 

Tic-Tac-Glow unlockables:
Reach the indicated amount of point on the indicated level within the time limit:
Tic-Tac-Glow Challenge: 75 points in the "Dazzle Shine" level
Sparkle Shine level: 50 points in the "Glimmer Shine" level
Dazzle Shine level: 75 points in the "Sparke Shine" level