As you all know, Mokuton or wood release is the ability the first hokage had that allowed him to create trees and forests with chakra.
http://www.mangareader.net/naruto/545/13 This is when Naruto was fighting the zetsu's, his Kyuubi chakra turns them back into trees.
http://www.mangareader.net/93-56332-...apter-505.html This is when he sprouts leaves beside Yamato after first controlling the fox.
I got this idea when the real edo Madara got Resurrected. Although we cannot say if Hashirama killed Madara, we can say that he had the upperhand in their last fight, even with Madara having the rinnengan. Its the only technique i can think of that could allow Naruto to overcome Madara/Tobi.
Also, my idea of how he would unlock it is since the portion of the kyuubi's chakra naruto obtained slightly creates a mokuton effect, maybe if the Kyuubi fully cooperated with him and worked with him as a team Naruto could get the full power of Mokuton.
http://www.mangareader.net/93-31099-...apter-462.html here Madara sais he can "see" the first hokage in naruto. Could this be foreshadowing Naruto gaining the power of Mokuton through cooperating with the Kyuubi?
What do you guys think?