[@Mr Allen J]
oh well sooooorrrryyyyyy, i'll edit it to Semiiiiiitiiiiic mister political correctness
one way or another get yo damn facts right and check yo privilege
"Jewish" is a word that can denote both ethnicity and belief and nationality and i'll be fucking damned if my guy and his family weren't Jewish by ethnicity and belief.

[@Estylwen]
> What if I tossed in anti-matter? Nuclear bombs? There is no end for your adaptive regeneration, and that makes you a god.
Yes, I love having powers that have a big development potential. But me being a god wholly depends on your good sensibilities.
His regeneration has limits on which I will elaborate a bit later and, of course, he can't regenerate if he is killed outright by the attack - and it'd be sensible to judge that an atom bomb or antimatter explosion would just outright annihilate Better and leave him a very much unalive smear on the ground - in one superhero fiction I've read, a regenerator kinda like Better was defeated by flash-freezing him and keeping him frozen in a block of ice. In order to adapt, he first needs to survive - and if he survives an atomic explosion or some extremely massive damage, it will still leave him in a sorry, horrible and slowly healing state in which he is easy to contain and finish off or imprison. Next, a singular exposition to a threat, even if it was so brutal, won't make him completely or even nearly immune to it - to become truly "adapted" to such a rare and unusual thing as a nuclear explosion and all that it entails, Better would probably have to...
Somehow carefully expose himself to bigger and bigger amounts of radiation or regular basis, casually subject himself to EXTREME levels of heat and suffer through drastic and sudden pressure changes to simulate the blast's effect on his system, I guess. So basically him developing new adaptations and the time those take to grow is mostly up to you - and also I personally have no idea about how he can adapt to, say, aforementioned antimatter attacks, except for maybe just GROWING in volume so that antimatter won't destroy him entirely. Similarly, he is never *immune* to bullets, fire or electricity. Small arms won't do jack at this point, yes, but they also don't just ricochet off like you're shooting Incredible Hulk - sustained fire can chew through his limbs or dense flesh and damage some vitals, and a precision shot in his eye will blind it for some time. Explosives, napalm, bigger guns - they all are still pretty effective at stopping Better's advances or even incapacitating him, even if such measures probably won't kill him unless the guy is shot apart until nothing remains or stuffed into a container full of white phosphorus and lit up. Similarly with electricity - he is impervious to small jolts that can make a weak heart skip a beat or even stop, yes, and he won't be KILLED by a powerful current in a thick cable - but it will seriously char him and overload his nervous system and leave him p much disabled for some time. 
Plus, considering the toughness of this fuckin animal, you can hinder him in much more serious or intricate ways than what others can handle. 

Another variant, btw - I can make him a bit younger on his timeline and not as "evolved" and instead see his progress and adaptations take place in-game. Though that takes out a lot of his hexapodal, bestial, sentient monster charm.

Also sorry for the wall of text. I understand the concerns. It's just that for me, the ability that makes me only resistant to one thing at a time and completely nonresistant to all others kinda defeats the purpose of this power. I'd like to argue to at least get a set of slowly improving resistances against all that I encounter and adapt to rather than ability to no-sell any single thing and be vulnerable against everything else.