Mirror Shards are an item in Kirby & The Amazing Mirror. There are eight Mirror Shards in total, in 8 of the 9 areas. Mirror Shards are dropped by bosses when defeated. When a boss is defeated again, a Maxim Tomato will appear in place of the shard.
As the pieces are collected, the Mirror Shards will gradually mend the Dimension Mirror. Once the final piece is collected, the Dimension Mirror will be fully restored, granting Kirby access to it, and the final areas of the game.