... If anyone's thinking of making a request, remember that a request doesn't have to be a named character from another series. I can work with a picture, a list of disconnected Aspects, four Powers that you wouldn't normally see together, whatever...
Well, THIS is an interesting notion.
I'm not sure it takes me where you wanted, though... I'm going much more thematic than wanting mechanics.
Like: OK you can slap together some disparate Aspects/Powers, but really it's the "fluff" and the RP that makes these combo's come alive. Asking you to just "do the mechanics" seems like... kinda not to the point?
Still.
It's an interesting thought. Like put in a "Demonic Co-Pilot" (literally a demon) and maybe 1-2 other "downbelow" powers, AND some TrueFaith powers like Righteousness / Holy Touch / etc. The character is tugged both ways, trying to balance on a cusp.
OK, let's try this... It's actually based on a character I've considered writing as fiction.
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Donatien Diaz was born to a single mother, somewhere in the US southwest. She was a good Catholic girl, and her family held her in disgrace for this.
She had been pursued by a wealthy man, but she resisted his suit for two reasons -- the one her family accepted was that he never actually offered marriage (only a wealthy lifestyle and vague assurances). The real reason, the reason in her heart, was that he made her profoundly uneasy. She didn't know why, but some part of her could not trust him; and her heart knew true: He was a warlock, and she had some sense that told her that
Something Was Not Right with her suitor.
In the end -- after she finally broke it off with him -- he summoned an Incubus (not a Whampire, but an actual NeverNever/Hellish/etc Demonic Being) to seduce her and ruin her. The supernatural wiles of the demon succeeded where the warlock had not.
Donatien is the child of that union; the blood of Hell (or somewhere else violent, powerful, and inhuman) runs in his veins.
In the years that followed, his mother became more and more religious, AND became rather supernaturally clued-in. Eventually she was able to be certain that her seducer had been entirely-inhuman, and suspected most or all of the truth.
But Donatien is her son, and she loves him, and she raised him as best she can. She raised him with love and with Faith... and it stuck. But eventually, she retired from the world and took holy vows. She lives as a nun, now, in seclusion. She sees only her Sisters in God, and her son.
He struggles, now. He's "more" than human, and he realizes this; he doesn't know the whole truth, but he knows that his mysterious father is the source of it all, and Bad News; he also knows that there is real refuge in Faith and in Love (and has figures out that "sex" is NOT "love" -- although this remains a major area of temptation for him!).
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As I originally conceived the character (as a fiction-writing project), Donatien had the free will of humanity and the limitless potential thereof, and ALSO the blood of Hell in his veins, with temptations toward the Sins (especially Lust, of course (given his father) but (courtesy of his "free will") ALL of the Sins). If he engages with the more-than-human powers within himself, he moves more towards becoming one of the Fallen and looses his ability to resist... looses his Free Will. Only by pursuing Virtuous actions can he draw back from these temptations and from finally Falling himself.
I see this (as a DFRPG project) likely borrowing from the "Changeling" rules a bit -- the "Choice" to become faerie or mortal (in his case, demonic or mortal).
Also maybe the "Laws of Magic" rules, where getting a "Lawbreaker" stunt makes it easier to get more and more...
But maybe it just needs a "Demonic Stress" track like a Whampire's Hunger -- he uses Hellpower, he takes DemonicStress, and it gets harder to be Virtuous and pull back (but I really like the longer-term implications of Stunts, instead of just a quick-fix "stress track" sort of consequence)...
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So... Is this enough to work with? Have I postulated too much that's not really Dresdenverse'ish / DFRPG'ish or needs custom stuff to work?