Generic Bakugan
All of the main characters in the anime own Bakugan that are implied to be one-of-a-kind (or at least extremely rare to the point that they are only ever seen used by one person). Background and minor characters, on the other hand, use Bakugan that appear to be fairly ubiquitous. These Bakugan are often used to fill space in large-scale battles. They were also used by a majority of the characters in the first half of Season 1. Every season uses a different set of these "generic" Bakugan, with the exception of Mechtanium Surge, which mainly uses the same ones as Gundalian Invaders. Some of these Bakugan also carried over from Season 1 to New Vestroia.