Only Mostly Dead: The Gods of the High Noon Skinline
So High Noon Ashe's bio says that human settlers Manifest Destiny'd so hard they destroyed Heaven, screwed over everyone ever, and killed a bunch of gods.
But it never says humanity got rid of all of them.
The Man with the Grinning Shadow mentions "a reclusive gunsmith rumored to be a fallen deity," for a start. But it'd be a short post if I stopped there, so I won't.
In the same story, Reverend Karthus says "The world is old, but many of our gods are still alive, watching over their progeny even now."
Now it's easy to dismiss that as him not getting the memo about Heaven being utterly and permanently wrecked and most of the gods murdered, but then he goes and does magic. Magic that, as I mentioned in a previous High Noon Karthus thread, is almost definitely not infernal. Magic that can suppress a demon.
Now what could the source of that magic be? Who do you think would have a very strong interest in maintaining at least some influence over the world, especially the kind that can be turned against the enemy? Who might want to make some devils pay without being terribly nice to humanity in the process?
Someone with a grudge against both, that's who.
I think his power came from a fallen deity who was severely weakened by the destruction of its home realm and reduced to working indirectly through mortals. Heck, there's probably more out there doing the same thing.
And wouldn't it be just the West's luck that one of the few survivors of their idiot decision was a god of necromancy.