Did you notice Obito healing his right arm? It must be some sort of Zetsu/Hashirama DNA mixed in because it seems that he's lost his arms a few times already (fight vs minato, fight vs fu and torune, fight vs konan). This also explains why he could use Izanagi, which he probably learned from Madara and the uchiha scrolls. Madara obviously survived against Hashirama and was in hiding probably in the dimension where Kamui takes you, and was conducting experiments with the tissue from Hashirama.
And have you noticed Zetsu looks like Obito, and is a yin-yang (black white) look like he is mixed with half of hashirama (white) and half of something else like uchiha blood (no eye obviously). Probably one of Madara's experiments before he passed.
And where the hell is Naruto? Is he somewhere storing some crazy amount of sage mode, or is he waiting in the other dimension so he could give Obito the okee-doke.
Here's a theory I also think Madara and Obito may be related that's why they both ended up in Kamui-dimension when obito got crushed and activated the Kamui, or maybe Madara had been watching obito for a while and saved him after everyone left him after being crushed for dead. He may have sealed a part of himself in Obito (like orochimaru), that's why he doesn't care to be called Obito anymore. He also referred himself as the Second Sage of six paths after his fight with Konan, and Madara said he unlocked the rinnengan before he died (probably through his experiments with Hashirama dna) which would be the second to have the eyes. He then had Obito/Madara to put his eyes (uchiha eyes) in Nagato who was a senju bloodline to awaken the Rinnengan, and that's why tobi/obito/madara called Nagato the third sage. This makes you think that Obito had Madara's real body stored somewhere if Nagato was suppose to bring him back to life.
For the fight against Minato and Tobi. I thought the same thing that Obito would be too young to be fighting Minato, because I remembered in the manga kakashi and guy looking very young. But when I went to rewatch the anime episode Kakashi and Guy looked like they were in there early 20's, which would make it more plausible that the masked man was in fact Obito. Also a lot of people were wondering how Obito was able to match up to Minato, but if you watch the fight Minato beat him pretty easily without getting a scratch on him.
Sorry for this long rant but I've had all this anticipation built up thanks to Kishi and his damn cliffhangers every week and needed to let some stuff out. This is all just theories I would like to hear your thoughts.
