Gon transformation in Hunter x Hunter Episode 131 – Anger X And X Light, that made his body mature around 20+ years, and most likely made him the most powerful person in the world, could have been achieved by Gon going through 4 of the five stages of grief multiple times.

What episode does gon turn into a monster?

Anger × and × Light. Gon goes beyond his body limits to achieve monstrous power.

What episode did Gon and killua turn black?

Why do Killua's and Gon's skin tones change in episode 45 and 46 Huncyclopedia? - Anime & Manga Stack Exchange.