King Dedede learned about Tabuu's motive and that his Off Wave would turn everyone into trophies. These brooches were created so that the fighters would change back from their trophy states even when there is nobody to revive them. They were placed on Luigi (whom he ambushed), Ness, and Zelda/Peach (although it seems he intended to use the third one for himself). After stealing their trophies from Wario, Zelda/Peach were taken from King Dedede by Bowser in a surprise ambush. Kirby then found the brooch and swallowed it, gaining the benefits of it when he was turned into a trophy in Subspace. If King Dedede had forgot to made these, then all of them would have been doomed and Sonic, and to a lesser extent, Jigglypuff, Toon Link, and/or Wolf would have had to save everyone, as they were not