These small, shiny treasures can be exchanged for goods at the Maze Shop.
Simply play the Dark Maze when it unlocks at Player Rank 20 to collect them as rewards. Then take your Bits over to Alf Underhill at the shop to spend them! The Maze Shop has an ever-changing selection of Hero Pieces, Awaken Zibuls, and Rainbow Sprites, so make sure to check in often and keep collecting those Shiny Bits!