Star Piece (Paper Mario series)

Super Mario RPG: Legend of the Seven Stars

In Super Mario RPG: Legend of the Seven Stars, the Star Road was broken up into the seven star pieces. Most of Mario and co.'s journey was based on finding the aforementioned star pieces, which in itself often required Mario, Mallow, and their friends in defeating a powerful enemy.

Paper Mario

Star pieces took on a new role in the 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?