My main villain would be Lucifer who gains immortality by turning his body to a sentient mass of energy — and following the first law of thermodynamics, energy can't be destroyed (or atleast that's what im trying to potray). However, MC, a man of science, will use another part of the thermodynamic law saying that energy could still be converted. So eventually MC will convert Lucifer to another form of energy that causes explosion, thus scattering his conciousness far away. But of course im open to possibility of another ways to defeat him. The problem is i haven't read much story with immortal villains, so the only example i could think of is Kars from Jojo's part 2 where he was thrown away to space by an errupting volcano and is cursed to float in the space without being able to die. Any other examples i could look up into?