Boss Endurance and Cake
By completing the game you can unlock Boss Endurance mode for Minigame and a Cake for your collection.
Boss Endurance: Complete the game once.
Cake for collection: Complete the game once.
Time Attack Mode
To unlock Time Attack mode you must collect all 120 chests throughout the game.
Hidden World
To gain access to the tower in the center of the World Map, collect the secret map pieces from each of the other worlds. In the tower, you can get any ability bubble, including the Triple Star Rod.
Hidden Birthday Message
On your birthday, play the game. After the startup sequence, there will be a brief 'Happy Birthday!' message decorated with various Kirby characters.
Get Special Abilities
To get some special abilities, you need to do the following:
Fire Sword: Mix fire and sword (sword scroll needed)
Ghost: Get all of the pieces for the Ghost Medal and then beat the ghost mini boss (you will find him randomly instead of another mini boss).Then inhale him.
Ice Bomb: Mix ice and bomb (bomb scroll needed)
Ice Sword: Mix ice and sword (sword scroll needed)
Thunder Bomb: Mix lightning and bomb (bomb scroll needed)
Thunder Sword: Mix lightning and sword (sword scroll needed)
Triple Star: Beat the boss on area 8 (the one before the final boss) he will drop the Triple Star ability that you can use
Extra Mode
To unlock extra mode you must collect all 120 chests throughout the game.