I recently started reading in RoP: The Infernal, and stumbled across mentions of Infernal Ghosts. Only now did I realize that this would be a great option to include the supposedly dead infernal parens of one of my players in the saga. Yet, I can't seem to find anything about them in the book - are they just another kind of demon, and not actually ghosts of dead people?
I was thinking along the lines that the parens tried to achieve immortality (just like his filius is now), and did this via the ghost route (like described in The Mysteries), only with an infernal touch. Would this work? Another thought: could he turn himself into a demon to achieve immortality?
As I understand it, there are "ghosts" for each realm of power, and canon does not state whether or not they are the souls, spirits, or echos of real people. Your player might be able to turn himself into an "infernal ghost", but he would have to leave the magic realm and have the source of his powers come from the infernal realm first, in my reading. As to the second, I don't think he could turn himself into a demon. At "best" he would be able to become an "Infernal saint", but then our information for that comes from Hell. Sure, they may be based in deception and lie to everyone else, but you're too smart for that to stop you, right?
Okay, found it - p.36 in RoP:TI. I was slightly bothered by the lack of an index.
I'll see if I can combine this with the Living Ghost option from The Mysteries Revised.
Remember this is for the infernal parens, though, not the player - I guess he'll go the "classic" route of an alchemist.
I'm sorry, I got a little confused, because of your worries about it working. For the "Mentor ghost with infernal taint" don't worry so much about the rules. If it's connected to Hell, it's a lie, one that cannot be detected. Just make it a demonic projection. If it's a ghost, some nitwit will try to harvest it for vis.