Fourth Dimension Space

From the Sonic News Network, the Sonic Wiki

Fourth Dimension Space is the final game board from Sonic Shuffle. It is the realm where dreams are kept: the whole domain will cease to exist unless Void is stopped. The entire board is built on the inside of a giant sphere, which makes navigation a tricky affair. Falling stars will periodically bop random characters on the head: return the star to its home in the night sky to complete the Quest and earn an Emblem. (This is the only Quest that can be performed more than once per game.) Complete the stage to initiate the Void Battle minigame. if the player comes first, the next cutscene is shown, followed by the final cutscene, and then the end credits.