From Sonic Retro
The Precioustone (プレシャストーン) is a mysterious crystal from Maginaryworld formed with the essence of everyone's dreams, which plays a key role in Sonic Shuffle. Typically, it is protected by Illumina within the Temple of Light, and is necessary for Maginaryworld to exist.
When Illumina split into Lumina Flowlight and Void due to her self-doubt, Void seeks out the Perfect Precioustone to become whole, only to shatter it and scatter its fragments to five locations, causing Maginaryworld to fall into disaster and corrupting the worlds due to Void's darkness. Lumina brings Sonic, Tails, Knuckles and Amy to Maginaryworld to collect the fragments and restore the Perfect Precioustone.
When the heroes almost complete the Perfect Precioustone, Void tries to go after it again, but is stopped by the heroes. However, the light does not return to the Precioustone, and Lumina loses all hope, but Sonic and his friends restore her faith and make her accept Void for what he is. This leads to Lumina and Void merging back into Illumina, completing the relic.
Gameplay-wise, the Precioustone fragments function like Stars from the Mario Party series. Players go around the board and try to collect as many as they can, with the game ending once all fragments have been claimed by the players (between 2 and 7 in VS. Mode, but always 7 in Story Mode). Upon reaching the Precioustone, a player must battle a monster, and should they win, they get the Precioustone, causing another one to spawn somewhere. The player who is furthest away from the Precioustone when it's collected will be crushed by a weight dropped by Dr. Eggman, taking away some of their Rings. At the end of a game, players are awarded an Emblem for every Precioustone they collect.