Aside from Metal Face, MF has also meant Metal Fingers. He's also Viktor Vaughn and King Geedorah.
As far as rap schizos go, I think Kool Keith/Dr. Octagon/Mr. Gerbick/Dr. Dooom/Black Elvis/Keith Turbo/Robbie Analog/Keith Korg/Spankmaster/etc., etc. takes the cake.
Both have done weird interactions with their different personas: Dr. Dooom killed off Dr. Octagon, while Viktor Vaughn's girl was cheating on him with Metal Face.