I see now, maybe the characther that can fake to be an NPC would be like a shadow momnster or something but would be extremely hard in nightmare mode thanks to the fog effect it have.
The harpy attack is a really change of fresh air, we need more ways to avoid being devoured, maybe we could add some sort of "dash" move to avoide the attack but also, in my opinion, the concept could fit to an arachne monster girl as well. It would walk on the ceiling all the time so it would be hard to see but do a little "tickticktick" sound when nearby, and when it saw you it it would fall on you and swallow you. I think that the arachne would have the slowlest time to digest you because it would enter in a sleep state after eating something.
Maybe it would be that the ghost will be actually just hunting for you and will not get distracted with another NPC... just to avoid more coding to it? I mean, kinda fits what a ghost would do, and maybe when it would be some sort of allie when we another pred is chasing form us.