I'll bet you mean "Bakugan" and if so, it's an anime show where these creatures from a different world called "Vestroia" fall to Earth with game cards and they can only be in the form of a ball except for when you're playing - that's when they can show they're true form because when you battle, it creates a link between our world and theirs. It is the most awesome anime show ever and you should TOTALLY watch it!