Hey everybody, lets bring the Tobi=Obito theories back. He seems to know both Gai and Kakashi. Obito is made at the leaf and Uchiha because no one came to get him out of that cave.
Food for thought, if its obito then the phasing ability from his eye could not yet be used by a tobi to phase him out (direct contradiction). Next choice is zetsu, he is master of traveling through ground but that fundamentally changes the tobi/zetsu dynamic we have already while shoehorning madara into an already shaky timeline. Any of the enemy ninja around could have recovered the corpse and then kishi will punish us with more chapters of flashbacks of how obito recooperated and blah blah. Best chance is the trauma of onsetting death awoke his MS in miracle fashion, allowing his crushed vitals and portions of his trapped body to be incorperal so to speak, and thus he mysteriously walks away into unknown destiny, short one eye.
_____ Obito is Tobirama's great grandson. The proof is in the pudding.