xavier was the one who orginaly stoped multiple man in his first apearance when he battled the fantastic four and god damned nearly won agaisnt them. i think it was only throguih xavier shutting of the dupes minds that alowed them to win
since mutiple man can talk to his dupes via telepathy, shouldn't making duplicates allow him some protection against xavier? I never read the one where FF fought the multiple man. I wasn't an FF fan. But how did multiple man manage to put up a fight. Did each of his dupes have super strength?
He can sense that they're around to a certain degree, but I don't think I've seen Jamie communicate with his duplicates via telepathy. In the Fantastic Four comic, his powers were going out of control as his suit ceased to do it's job of negate the kinetic energy he makes contact with. He didn't fight the Fantastic Four per se, but was there for help in containing his powers.
All duplicates do not have extra super strength, but he has a certain resistence to mind control with fewer dupes. But the more dupes he has the more susceptible he is to mind control (i.e. Mastermind's daughter controlling him during his term with X-Corps). Xavier's telepathy, however, is too strong for Jamie to handle. He asked Jamie to create duplicates for him to use as an extension to his own powers, so he's shown to be penetrated before (of course in that scenario, Jamie willingly allowed it).