A parasitic mold with an unusual lifecycle and powerful mind-control properties.
Sometimes walking through a moldering old crypt can be a pleasure. With the smell of bone dust and ancient burial wrappings, almost like a library. Certainly as quiet. Until you step in a patch of Choo Mold.
A cult's theology is binding on the god involved: it is possible for that god to believe (and see, just like Winston Smith in 1984) that other gods are mythical, or jumped-up demons, or failing older spirits, even while those gods actually exist and thrive and act in the cosmos, even while working against him.