Supreme Ultimate Rasengan
Presumably my guesses go to Minato & Naruto combining/fusing their Rasengan to one, forming the Supreme Ultimate Rasengan, to deal some massive damage to the Juubi. Unlikely to Madara as he's drowling all over Hashirama.
Alot of you will reconsider that, saying that Kishimoto won't use some supreme 'badass' jutsu based of a Shippuden movie.
I have my stakes.