Metamorans are the inventors of the Fusion Dance, a technique that allows two sapients to combine into a vastly powerful, solitary being. They played an brief but important role in the survival of the entire universe: Goku met them in Heaven at some point between what are considered the Cell Saga and the Majin Buu Saga. This could be compared to how Goku learned the Instant Transmission technique from the Yardratians.