Unlock Waddle Dee
Beat the game once.

Unlock Jump Game
Complete the game with all five characters.

Unlock Bead Line
Acquire six medals.

Unlock Course 1-8
Acquire nine medals each.

Unlock King Dedede
Acquire twenty medals.

Unlock Life Boost
Acquire seven medals.

Unlock Life Boost
Unlock twelve medals.

Unlock Life Boost
Acquire fourteen medals.

Unlock Meta Knight
Acquire twenty-five medals. King DeDeDee must be unlocked first.

Unlock Song One
Acquire three medals.

Unlock Song Three
Acquire three medals.

Unlock Song Two
Unlock three medals.

Unlockable: Block Attack in Subgames
You must beat level 2 of Block Attack in Boss Games.

Unlockable: Cart Run in Subgames
You must beat level 2 of Cart Run in Boss Games.

Unlockable: Paint Panic in Subgames
You must beat level 2 of Paint Panic in Boss Games.

Unlock Waddle Doo
Insert Kirby and the Amazing Mirror (GBA) into slot 2 on your DS after unlocking the other characters to unlock Waddle Doo as a playable character. You can also just complete the game with Kirby, Waddle Dee, King Dee Dee Dee, and Metaknight to unlock the fat guy.