When starting, you will have a choice of Uncommon fighters that can be found at the following locations.
Fighter
Location
Dr. Saiphon (Lightning)
Bamboo Forest.
Grandmaster Yong (Fire)
Fire Temple.
Jim Karateman (Earth)
Bamboo Forest.
Under Earth Champion (Water)
Subterranean Village.
Yak (Shadow)
Deep Caverns.
Fusion
Combe two of the same fighter to create a stronger character. You can continue to fuse stronger characters together to eventually end up with a rare fighter. Eight identical characters are required to obtain maximum stats.