From Kirbypedia

English Name:	Mirror Shard
Japanese Name:	鏡のかけら Kagami no Kakera Mirror Shard
First Game:	Kirby & the Amazing Mirror
Type:	Collectable

An item in Kirby & the Amazing Mirror. Kirby must collect all eight pieces that have been scattered across the Mirror World. Once they are brought together, they open the Dimension Mirror and allow the final battle with Dark Mind.

When Meta Knight flies into the Mirror World, he is confronted by a shadowy double. It defeats him, traps him in the Dimension Mirror, and then cuts it into eight pieces. One is held by a boss in the different levels.

Collectibles

Sparkling Star - Rainbow Drop - Crystal Shard - Mirror Shard - Heart Star Boss Battle Badges - Copy Palette Style - Ghost Medal - Graphic Piece - Musical Score - Secret Door Key - Secret Map - Sound Player - Spray Paint - Star Seal - Strawberry Shortcake - Treasure Chest - Vitality Piece