Star Piece (Paper Mario series)

A star piece is an item that can be used to trade. There's 160 in Paper Mario and 100 in Paper Mario: The Thousand-Year Door.

In Paper Mario, they are used for trading with Merlow for badges. In Paper Mario: The Thousand-Year Door, they are used for trading with the creature Dazzle in Rougeport Sewers. You don't get anything for finding all of them in PM2, they're just for Dazzle's badges. Perhaps in Paper Mario they can be used for something else?