I mean, prize container was supposed to hold dead monster remains , but here fairy pops out with just some parts of limbs missing and owns superpowered human like it's nothing. Monsters definitely aren't as dependent on the body as humans, I'm guessing as long some kind of core is intact(which might be in whole other place or dimension from the body), they will revive with time and restore any physical harm to the body/vessel. Even more so for the body morph types. Obviously, this effect is much weaker in infected humans, I'm guessing brain and maybe heart will count as vital, kinda like vampires, but everything else is fair go. And humans with energy types would need some kind of life support if they sustain certain amount of injuries, like those liquid stasis tubes or something, otherwise regeneration would be slower than remaining tissues dying off.
Electricity effect on mc was a bit weird, though. It looked more like a catalyst for monster part in some scenes than anything else, with explosive tissue expansion. Going for weakness on progenitor monsters could backfire hard.
I agree about Michael getting powers could go horribly wrong, but that's what friends are for - to keep you sane. He is already crazy adrenaline combat junkie, and the way he's going, he will either break mentally anyway or die while going up the ladder of monster opponents. If he tries to get power, he will already see the "end-tier" content to aim for, no reason to go crazy and lash out at people nearby. From then on , it's just a matter of control and discipline, and that's something martial artists have in spades.
You can worry about Michael when he finally kills strongest monster, but I doubt that will happen any time soon