After Beating Story Mode, defeating the Final Boss of Royal Road, and watching the Credits, the next you enter Story Mode, the game will show a message saying that you've unlocked the "Copy Ability Testing Room". While Kirby is near "Fine Fields" on the World Map, press down to enter the "Copy Ability Testing Room". The "Copy Ability Testing Room" is an area filled with rooms that have all of the game's Copy Abilities. There is also a Metal Waddle Dee and some tiny Star Blocks that Kirby can use to practice his Copy Ability. You can also come here to grab a particular Copy Ability, leave using the Warp Star, and keep it so that you use it for certain Stages.