Sketch:
Phase Sans is quite strange... Anything that could possibly kill him will instead phase through him instead of hitting him. Trying any way to kill him is futile because he phases uncontrollably. Basically meaning that he can't control what does and doesn't phase through him. The only way he can truly die is if he starves, but even that is a problem. He doesn't eat normal food, the only thing that can sustain him are human souls, he can eat any type of human soul but he perfers the red ones. This, if course, would be a problem in the Undertale Multiverse. Although what makes it even worse is that Phase Sans is a good person. They want to be friends with everyone and he wants to help him and his brother Papyrus find a new home, but because of his dietary needs, that's almost impossible. Wait, I said "new home", what happened to their old one?...
That's something you'll know soon.