This is exactly the kind of stuff that makes a manga bad. I mean, I know Kishi wanted to give Minato a powerup, but come on, Sage Mode would have worked much better from a plot perspective.
The rules on Kyuubi Mode or Bijuu Mode, whatever he has, had been established before, when Naruto trained at the waterfall of truth. He had to defeat his evil side, then battle and beat Kurama, and absorb his chakra.
So how come Minato, who hasn't done any of that, and who died instantly when he sealed the other half of the Kyuubi inside himself, can now use Kyuubi Mode perfectly? And please don't give that "he is a genius argument", because that is just bull****. No matter how smart or skilled you are, you can't just go around breaking already established rules.
