Oro was the main antagonist in part 1 the dudes trash now, i thought Tobi was the main villian now i lean to Madara or Sasuke, Oros being used for Sasukes sake after this hes gone.
I think Orochimaru or Sasuke. Orochimaru was way too prevalent even when everyone thought he was gone for good, and now he's back. If Kishi seriously brought him back just to help Sasuke after revealing that he knows all of Madara's secrets and even the slight hint that Orochimaru left a curse mark on Madara, that would be some shitty ass writing.