The Ghosteroid is a massive planetoid-sized Ghost of unknown origin that appeared in Pac-Man and the Ghostly Adventures and was the main focus of the episode Planet Pac Versus the Ghosteroid.
The Ghosteroid was first spotted by Sir Cumference through his telescope and was quite horrified to see the Ghosteroid heading for Pac-World. It is later revealed that the Ghosteroid was summoned to Pac-World by Dr. Buttocks and his tractor beam so it would annihilate the surface and the Pac-People and give Betrayus the opportunity to invade. However after Butt-ler discovers a fatal error in Buttocks's plan, Buttocks realizes that the Ghosteroid will not only annihilate Pac-World, but the Netherworld as well. Betrayus then tries to destroy Buttocks's machine to stop it but doing so instead leaves them with no chance of making a repulsing beam to move the Ghosteroid away from Pac-World. This forces them to cheer for Pac-Man and his mission to defeat it.
Once Pac-Man reaches the Ghosteroid, he evades several of the Alien Ghosts that protect the Ghosteroid and then uses the new Power Berry given to him by Sir Cumference, which causes him to transform into Planet Pac which then chases the horrified Ghosteroid and eats it whole while enjoying its exotic alien flavor. He then spits out its eyes and bits of slime, and the Ghosteroid's remains are left to drift through space, defeating it once and for all.