I'm of the mind that the Black Goat doesn't truly exist.
The entire game is told from the POV of someone with stated mental issues (aside from one brief moment). Mae has a massive migraine at the second investigation, which could easily be caused by stress. Considering when the dreams started, I think they're stress dreams. As for the cult, I think the first guy brainwashed the others into thinking there was something in that hole that was saving the town when one day he killed his friend and threw him in, and all of a sudden the town had a burst of prosperity.
It's ambiguous, yeah, but I think the Black Goat didn't ever exist. Maybe what's "coming your way" could just be Mae finally having to own up to being an adult now.
or hey maybe i'm rambling about unrelated shit