The First Challenge

is episode 155 of the Naruto: Shippuden anime.

Synopsis
Naruto is now at Mount Myōboku. He receives a false alarm from Gamakichi saying that he will turn into a frog as a risk of undergoing senjutsu training, however Fukasaku straightens that out. Fukasaku then informs Naruto he has a risk of becoming a frog if he takes in too much natural chakra but he then assures him there is no need to fear since his Fukasaku's baton has the ability to knock the natural chakra out of anything as long as there isn't too much intake. To expedite the process of becoming a Sage, Fukasaku rubs some oil coming from Mount Myoboku on Naruto so he can take in natural chakra and become familiarized with it before the real rigorous training of sitting still to take in natural chakra. Since Naruto quickly begins frog transition, he comes up with an idea of using shadow clones to gather information so his training process will become even faster. However, since Fukasaku had trouble coping with all the clones, Naruto's numbers were narrowed down to only one. After hard work and revelation that only those with high chakra reserves like Jiraiya and himself can undergo senjutsu training, Naruto finally begins to make progress making a slight but acceptable transition into frog form. He lifts a frog statue and sadly, topples them. Since they are Naruto's respected predecessors in the senjutsu training, the latter is ordered to rearrange them. Afterward they have a meal which Naruto reveals was delicious. He has doubts that he is becoming less human by the hour and when the meal is complete, Fukasaku hands Naruto Jiraiya's first book, 'The Tale of the Utterly Gutsy Shinobi'. Naruto reads it and after becoming emotional, he reminisces on a time where he and Jiraiya had a talk about world peace. The scene skips into the extraction of the tailed beast where Madara, Zetsu and Kisame realize that Sasuke has blundered and only acquired an octopus leg of Killer Bee's Eight Tailed form. Pain heads in to invade Konoha.