Crystal Stars
From the Super Mario Wiki
The Crystal Stars are the 7 objects Mario, Goombella, Koops, Flurrie, Yoshi kid, Vivian, Bobbery and possibly Ms. Mowz collect in Paper Mario: The Thousand-Year Door. They open the Thousand-Year Door to the Palace of Shadow and will teach Mario 7 special moves. They consist of the Diamond Star, the Emerald Star, the Gold Star, the Ruby Star, the Sapphire Star, the Garnet Star and the Crystal Star.
The stars were created by the Shadow Queen to hold the essence of the heavens, but the four heroes collected them and used their power against the Queen. One of the castles built to hold the stars is Hooktail Castle.
The stars bear much resemblance to the Seven Stars in Super Mario RPG: Legend of the Seven Stars.
