All the demons I've ever seen were rather different. But the corruption is -

- well. Not exactly a known phenomenon, I suppose. We really don't know much about it at all, other than that it's an alicorn-specific affliction of some kind. But it's been recorded for centuries, and alicorns have recovered from it before.

[In...a grand total of one case that he's aware of. Still, that's a start.]