How can Obito combine 4 different nature transformations?
Obito is the Jinchuuriki of the 10 tails. Having the blood of the Uchiha + having the Rinnegan and the Mangekyo Sharingan + being trained by Madara himself, Obito would have surpassed any living ninja in technique and chakra depth, as well as natural talent. It was even said at one time that he was the same as the "Sage of the 6 paths".