because he has "infinite" (or most likely really a lot) and, more importantly, free electricity thanks to his magic;
anyway the argument is moot because the story required him to do a sidequest so any loophole to make him "useful" doesn't really matter.
It's not really explained (or maybe I forgot) but I guess different types of undeads have different vulnerabilities?
Like a vampire is stronger but gets more vulnerable as "balancing" :thonk: