Defending his old man's honor like the good boy he is.
Naruto and company manage to hit Obito with the Amateratsu-Wind Shuriken combo attack, but it doesn't do any damage to Obito. Tobirama also notices that Minato's right arm is not regenerating, and that's because Obito now has some super-duper jutsu that nullifies all other ninjutsu including Edo Tensei. Naruto screams for more powerful to go into full Kyuubi mode, but Kurama pulls the plug on the fox chakra and tells Naruto that he needs some time to gather the juice, and this leads Tobirama to belittle Naruto as well. Gamakichi's summon time is almost up so he spits some slime at Obito which Obito blocks but the slime doesn't disappear. Gamakichi then disappears, and both Naruto and Tobirama notices that the slime did not get dissipated. Minato is feeling guilty now about not noticing that it was Obito who attacked the village all those years ago, and Obito seems to sense this and belittles Minato for being ignorant. While Obito busy insulting Minato, Naruto gathers energy to go into Sage Mode and forms a Rasengan. Tobirama then teleports Naruto right behind Obito and Naruto smacks Obito with the Rasengan. Obito is damaged and sent crashing to the ground, and so apparently Senjutsu still works against Obito.
Juubi-Obito is now so cheap that he has a jutsu to cancel all ninjutsu, but thankfully senjutsu is different enough so it can't be nullified. I'm not surprised to see Sage Mode making a comeback in important moments. I still see Naruto's ultimate form as being to use Kurama's chakra and Sage Mode together in harmony. Sage Mode alone probably won't be powerful enough to stand up to the Juubi or Rinnegan + Sharingan hacks, but Sage Mode plus Fox Mode would make things interesting.
In other news, Tobirama solidifies his status as an ass by belittling both Naruto and Minato. Of course, Naruto failing to transform was pretty hilarious, but Tobirama just isn't a nice guy and likes insulting people. He is pretty handy when it comes to fighting though. We'll see if Kurama's dark side emerging in the last page of the chapter will lead to.