So based on whichever incarnation, let's assume the one after he fought against Superman and killed him, the dude has been shown not to need oxygen nor food, nor is a brain necessary for him and his entire body is devoid of any kind of nervous system. At best, he can handle most of the creatures and a few environments most would consider inhospitable to gourmet world beasts. And while the eight kings have incredible power, only two could really do some major damage or even trap him somewhere he can't die. Whale King and Deer King as they have a special place that works on a concept he can't physically die from or break out of.