Hmm... Well, for one, they're actually from this world. At least, that's the impression I got.

[Too many things seem to stack up, like Luceti-born children gaining larger wings.]

And for the most part, they're insane. All they want to do is take people and use them in a ritual that kills them permanently. And during the last draft, they even dropped a Shift Bomb on us. We would've been goners if John hadn't stepped in.