Beat Candy Constellation, then go left as far as you can.Go into the door.Every Ability will be there except UFO, Crash, Cook andMaster.

Boss Rush Mode is on the menu

Metaknight's Sword will appear in front of the Magic Mirror once you've unlocked it

The Power Center door is in the main 'hub' of Rainbow Route (Area 1) in the top left corner and contains all of the Powers in the game

The Sound Test/Kirby Colors can be accessed through the Treasure List

Unlock - Action

Sound Test - Find the CD Treasure (Find Musical Scores to unlock new tunes in it)
Use Metaknight's Sword - Defeat the final bosses
Boss Rush Mode - Get 100% on a file
Different Kirby Colors - Find cans of Spray Paint spread throughout the game
Open the Power Center - Find and hit all of the Portal Switches in the different areas