Brooch

A brooch is an object featured in a few cutscenes of Adventure Mode: The Subspace Emissary in Super Smash Bros. Brawl. They are round, golden badges depicting King Dedede's face.

Story
Some time after learning of Tabuu's true nature and the power of the Off Waves attack, King Dedede designs three brooches, worried about the possibility of Tabuu turning every fighter into a trophy, with one of them being for himself. A brooch works like a countdown timer in that it revives a fighter from their trophy after a set period of time.

The brooches are first shown in a cutscene set in Castle Dedede, where King Dedede puts on a trophy of Luigi and Ness each. He reluctantly decides to put the brooch attached to him on to the Peach/Zelda trophy. After this, the ceiling starts to crumble and fall, and Bowser his minions raid the castle. Bowser steals the princess trophy, removes the brooch, and leaves. Some time later, Kirby finds the brooch and eats it.

In Subspace, when Tabuu's Off Waves turns every fighter into a trophy, Kirby, Luigi, and Ness are each revived by their brooch.

Trivia

 * It is said that King Dedede had plans to make a fourth brooch for himself, after applying his one to the princess trophy.