[@Vulkan] You would actually have to control his mind, because even if you used an illusion to "kill" him, he would be so used with the idea of dying that it wouldn't be much of a hassle, and since he is everywhere simultaneously, trying to make he believing that he is dead (Like "killing" him with an illusion, and throwing him in an void or something like that) wouldn't be effective, because he would just appear behind you smiling. I think that the only way for him to die is if he kills himself willingly, or if someone controls his mind