Café de Nuit

I was writing a campaign set in the Mountains of Misery, when I realized that I'd heard of some cult devoted to an cave-dwelling entity in said Mountains. Can anyone give me more information on that?

You're thinking about the Dark Delvers. There's some stuff in the Gaz II, but the meat of the info on them is in Forbidden Lore.

Can't remember much off the top of my head, other than they worship some entity called the Hated Mother who dwells far beneath the earth and that they have allied themselves with Ebb (and possibly Gloom).

Aha! That's them exactly. Thanks - this will really help the campaign. I wanted a villain who is totally inhuman, to contrast against the more-or-less-human vampire villain. Then the PC (there's only one...) gets to choose with whom she wants to align. It should be fun...