Kishi forgot to explain this

[Hexen]

he found the shikkotsu forest and trained...idk only reasonable situation

I'll consider it

 

[ᖇ α z m α η]

It was never explained what kind of sage mode he possesses [Ex: Toad,Dragon]...

He must've gained the ability to gather nature chakra during the war period [Due to being Ashura reincarnation de ability manifested due to constant war]

P.S. Ashura represents the body of the sage after all .​

 

[Angelic.]

kishi doesnt do too well at characters besides naruto and sasuke.

 

[Styles]

who said that was sage mode? Lol

Tobirama did(when he saw Naruto's SM) and Hashirama said ''Madara has taken my senjutsu chakra''