This area is a course in the Star World and is home to the Star World's King Bob-omb, Rainbow King. It is also the Star World version of the regular Bob-omb Battlefield.
In The Cosmic Crystals, Mario fought the Star World's King Bomb-omb. In TCC2, they search for the Cosmic Crystals, but have no luck. Tyler and his friend find the missing Cosmic Crystal on a Koopa and use it to make Tyler-Os better.