Originally Posted by Konnaha_yellow_flash
Obito already saw through his SG in kakashi as if they were still connected... Now his eye even in kakashi became Mangekyou as if still connected to obito still... And since zetsu said zetsu (hashirama plant bodies with use of his powers), can use telepathy... That means that obito should be able to as well...
Also, I think obito already has some relation to the younger brother of the sage either through the sunju or uzumaki... How else is it he is able to use hashirama's mokuton so naturally... and notice it was only him with the half body of zetsu/hashirama that was using the mokuton, not even the tobi zetsu body suit... which is why only the right side of his body used the mokuton... it was all him...
The eyes advancing doesn't require any wacky theories to be explained, see my earlier post. Obito seeing through his own eye in Kakashi is a timeless cliche.
Obito gained extreme capability with the Mokuton in a combination of the ways EdoMadara did and Nagato gained with the Rinnegan. He was fighting on pure emotion and instinct; the same conditions that led Nagato to awaken the absolutely insane extent of the RG's powers that he had. He also had the actual DNA of Hashirama connected to him fairly directly, just as Madara did. The probable reason it was his body's right half that was capable of acting is that the part of him constructed from Hashirama's DNA (the Zetsu body) is more readily capable of acting in synch with the Tobi body. Obito doesn't need to be genetically related to the Senju/Uzumaki half of the RS's lineage because half of his body is now completely constructed from Hashirama's DNA, giving him the connection intrinsically.