Event Mode Unlocked - when at the start screen, press z and start at the same time to have an event button pop up for games with two or four players

Code Effect - Press z and start at title screen event mode pop up

Skip Credits - When at the credits press Start + A, to skip the credits.

Artist on the Court Unlockables

Bowser and Bower Jr.'s painting Complete Diddy Kong's painting within time limit.
Diddy Kong's painting Complete Luigi's painting within time limit.
Luigi Painting Complete Mario's painting within time limit.
Yoshi's painting Complete Bowers and Bowser Jr.'s painting within time limit.

Balloon Panic Unlockables

Super Panic level Complete the Panic level.
Ultra-Hyper Panic level Complete the Super Panic level.

Chain-Chomp Challenge Unlockables

Famished Chomp level Complete Hungry Chomp level with the highest score.
Hungry Chomp level Complete Perkish Chomp level with the highest score.

Coin Collecters Unlockables

Coin Challenge level Beat the Gold Rush level.
Gold Rush level Beat the Jackpot level.
Jackpot level Beat the Fever level.

Colorful Yoshi

Yoshi's Defensive Power Shot Color Change Beat Flower Cup doubles with any character

Event Mode - At Mario Tennis title screen hold Z button while pressing start to unlock Event mode. This is a tiebreak game, you are able to select from 3,5, or 7 points. This does not remain unlocked however, you must do the code every time.

Get a character's star - To get a character's star version, just beat the 3 tournaments of the Normal Cup with a character and you will get the star for this character.

Gooper Blooper Unlockables

Master Blooper Complete the Rival Blooper level.
Rival Blooper Complete the Buddy Blooper level.

Mecha-Bowser Mayhem Unlockables

Iron Frame level Beat the Aluminium Frame level.
Titanium Frame level Beat the Iron Frame level.

Teeror Tennis Unlockables

Pesky Poltergeists Score 50 points in the "Goofy Ghosts" level within time limit.
Phrantic Phantoms Score 150 points in the "Pesky Poltergeists" level within time limit.

Tic-Tac-Glow Unlockables

Dazzle Shine level Score 75 points in the "Sparke Shine" level within time limit.
Sparkle Shine level Score 50 points in the "Glimmer Shine" level within time limit.
Tic-Tac-Glow Challenge Score 75 points in the "Dazzle Shine" level within time limit.

Unlock Ace COM skill level - To unlock the Ace computer skill level for play in exhibition, defeat Planet Cup in either Singles or Doubles mode.

Ace COM skill level To unlock the "Ace" Computer skill level for exhibition, defeat Planet Cup in either Singles or Doubles mode.

Unlock courts and special courts options

Bowser Court To unlock the Bowser court, just beat the Fire tournament of the Special Cup in singles.
Mario Bros Court To unlock the Mario Bros court, just beat the Thunder tournament of the Special Cup in doubles.
Special courts options To unlock all the options of a special court, just play on that court in the Special Cup.

Unlockable characters

Boss Packun (Petey Piranha) To unlock Boss Packun (Petey Piranha), just beat both Special tournaments (Fire and Thunder) in doubles.
Hana-Chan (Wiggler) To unlock Hana-Chan, just beat both Special tournaments (Fire and Thunder) in singles.
Patapata (Paratroopa) To unlock Patapata (Paratroopa), just beat the 3 tournaments of the Normal Cup in doubles.
Propera Hey-Ho (Fly Guy) To unlock Propera Hey-Ho (Fly Guy), just beat the 3 tournaments of the Normal Cup in singles.

Unlockable Infinite Challenges - To unlock the Infinte version of the Special Games (only some have them), do the following.

Balloon Panic Challenge Beat Ultra-Hyper Panic
Coin Collectors Challenge Beat Gold Rush Challenge
Gooper Blooper Volley Challenge Beat Master Blooper
Terror Tennis Challenge Beat Phrantic Phantoms
Tic-Tac-Glow Challenge Beat Dazzle Shine Challenge

Unlockable Minigames

Baloon Panic Beat the Flower Cup in Singles
Coin Collectors Beat the Mushroon Cup in Doubles
Mecha Bowser Mayhem Beat the Mushroom cup in singles

Unlockable Tournaments

Flower Cup Beat the Mushroom Cup
Moonlight Cup Beat the Rainbow Cup
Planet Cup Beat the Moonlight Cup
Rainbow Cup Beat the Star Cup
Star Cup Beat the Flower Cup
Thunder Cup Beat the Fire Cup