I think he thinks he can win, he hasn´t seen the "new" madara with rinnegan and new outfit, he doesn´t even know what rinnegan is.But does Sasuke really want to piss of Madara? he knows he can't win against him in a 1 v 1
Against sasuke with ems, yeah, i think he could make quick work of him, it was not a clone cuz black Zetsu was supposed to do something while white-Zetsu was guarding sasuke in case Kabuto decided to go there, besides, he had a half-face so it had to be the real one.Im guessing it was a clone, Zetzu wouldn't be killed off that easy