Star Cup
To unlock the Star Cup beat the 3 tournaments of the Normal Cup.

Hard Difficulty
To unlock the hardest difficulty level beat the 3 tournaments of the Star Cup.

Bowser court
Win the Special Cup Fire tournament in singles mode.

Mario Bros. court
Win the Special Cup Thunder tournament in doubles mode.

Fly Guy
Win all three Normal Cup tournaments in singles mode.

Hana-Chan
Win the Special Cup Fire and Thunder tournaments in singles mode.

Paratroopa
Win all three Normal Cup tournaments in doubles mode.

Petey Piranha
Win the Special Cup Fire and Thunder tournaments in doubles mode.

Star for character
Win all three Normal Cup tournaments with a character to unlock his or her star version.

Alternate Yoshi's defensive power shot color
Win the Flower Cup tournaments in doubles mode.

Mecha Bowser Mayhem mini-game
Win the Mushroom Cup tournaments in singles mode.

Balloon Panic mini-game
Win the Flower Cup tournaments in singles mode.

Coin Collectors mini-game
Win the Mushroom Cup tournaments in singles mode.

Wiggler
Beat normal flower cup in doubles, to unlock Wiggler (Defense).

Event Games
When you get to the main menu, push 'B' to go back to the 'Press start' screen, then hold 'Z' and then press 'Start' or 'A' and then Event games will be unlocked.