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 is Gon's rage?

Anger × and × Light. Gon goes beyond his body limits to achieve monstrous power. Neferpitou (Pitou) become overwhelmed by Gon's New power.

What episode does killua first transform?

Episode 119 (2011)