All of that falls clearly within Nen's stated rules, so it's all good. Don't blame Togashi for figuring out an extremely versatile ruleset.>Meruem gets btfo
This one I don't remember very well, but it doesn't seem farfetched given how chimera ants work in the first place.>Gon-san
He made a condition of never using nen again in exchange of using all his reinforcement right at that moment, perfectly consistent.>Aruka
It's a new element and his nen is clearly overpowered, but it's probably going to be explained if an when they finally get to the dark continent. Also, it didn't recover Gon's nen.>Hisoka>do we know about post-mortem nen? Yes, Chrollo mentioned it and made use of it during the fight.>can nen users upgrade their nen? Yes, Chrollo invented his bookmark.
What exactly is the problem? The only farfetched thing is that Hisoka's brain was without oxygen for a while, but we have no idea how long and how that works for this fantasy universe.