This is a video of the 4 secret characters that can only be unlocked with a gameshark.
Hamma Hamma, Qubeley, The-O and Zeta Gundam. Note: the gameshark characters are the ones on Player 1 side. Their names do not show up properly under the health bars. Why they weren't completely unlockable by normal means? I don't know.. they seem to be fine with no visible glitches.