Not a whole lot. The cult was originally based in Silent Hill, but recently it seemed to just dry up. It was right around the time Harry Mason was murdered... Hm. As far as what could stop it, I destroyed his physical body, which I think is what you do for ghosts. It seemed to work. I moved out of the complex pretty much right away, but I haven't heard of anything weird going on since then. I do know that he'd need to perform a ritual called the Ritual of Holy Liberation on the place he plans to use first, though. I don't know what it entails. Then there's the big one, the 21 Sacraments for Descent of the Holy Mother. It requires 21 people to be sacrificed, and each of them has some role to fill. My neighbor was supposed to be number 20, "The Mother Reborn" and I was supposed to be 21, "The Receiver of Wisdom".
Vampires? I think I'd have rather faced them than some of the things I saw in Walter's nightmare worlds... That's his name, Walter Sullivan.