It was never explained how his appearance changed between him disappearing and him returning in his new form. Would that have anything to do with the nebula gas or a similar substance to that? Lastly is it a similar process of corruption akin to how Fire Lord and his cronies came to be?
He rebuilt himself.
From his page on HS01.
Nah, obviously he hit the gym and got ripped.
If he’s made of metal can he really get get bigger by working out?
How did he (and Core Hunter, for that matter) manage to survive without a Hero Core? I’ve never understood that. Don’t they need one to function?
Maybe they still had their quaza cores inside, but separated them from the hero emblems? Or they found another way to function, just like all the other villains.
IIRC Quaza Cores “imbued the heroes with a keen sense of justice”, which as villains I could see them consciously rejecting in favor of a more standardized (even “civilian”) power source.
Maybe some illegal diet supplements as well…
On the subject of Von Nebula and Core Hunter surviving without their hero cores, since a core transplant is said to change the personality of any hero it’s done to, it does indeed seem reasonable that switching to whatever power sources every other character in the series uses could also bring about a personality change. This could help to explain why when HF’s own went bad, they went really bad,- seeing the cowardly Von Ness become the menacing Von Nebula, and Core Hunter going from thief/smuggler to life-source-extractor.
That being said, if more members kept leaving HF, would it stand to reason that the “New Personality Lotto” would eventually turn one of 'em into a teddy bear persona?