1. Hashirama Senju’s Sage Mode/Sage Training/Sage Master
This is another mystery. What kind of Sage Mode does Hashirama Senju use? Because it’s completely different from Naruto’s and Kabuto’s Sage Mode. Who do you think might eve taught sage Jutsu to Hashirama or did he learn it on his own. Also What training did Hashirama do to achieve his Sage Mode as its evident that its one of the strongest Sage Modes which has this awesome Jutsu (Shinshu-Senju) this Titanic wooden thing appears which can hold Kyubi in its palm.I’m wondering why didn’t Hashirama use it against the Ten-Tails.
2. Nagato’s Rinnegan
Well, we all know how Badass Nagato Uzumaki is, but we all also know that how the transplanted eyes work (example: Kakashi). So for Rinnegan/Sharingan to work at its best we need the user to have the DNA of an Uchiha or (Uchiha+Senju), or else just like Kakashi the usage of Rinne dojutsu will take a big toll on the user(hence Kakashi always covers his Sharingan). Uchiha’s brain produces a special kind of chakra that makes/powers the Sharingan. In the same way, Uchiha+Senju chakra(Raikudou) gives Rinnegan. As a distant relative of the Senju, Uzumaki Nagato only has Half of the ingredients for Rinnegan.