I'm playing a were-dragon who grew up the only non-magical member of a magic family - mom was a wizard, dad had psychometry, etc.  He kept borrowing his folks' grimoires and how-to books in an attempt to squeeze out some magic, but none of it worked - until he grabbed Advanced Self-Transfiguration.. Turns out he's a were-prodigy.

may have once been human, but by the time of the story, she wasn't human anymore. If I recall correctly, it says in-story that . That, plus her power, indicates to me that she is closer in makeup to a spirit or god than to a human.

We should probably specify for this discussion:  Divination can refer to precognition (seeing or predicting the future), postcognition (seeing the past), and farsight (viewing and influencing places far removed from the caster.  The divination focuses I posted before are generally intended for farsight and postcognition purposes, if only because precognition runs pretty close against the 6th Law.

The issue with that, Drachasor, is that being a True Believer and/or Champion of God isn't about being Religious, as I understand it.  It's about living the faith you believe in.  This is why Sanya, who isn't even Christian, has a Sword of the Cross.  I feel that if someone is acting as a champion of the faith but behaving in ways that are counter to the virtues specified in their faith, then they should at the *very* least get a heavenly messenger with a sobering wake-up call.

Does he change whenever he uses the sword, or only when he activates it? If it's anytime, Human Form doesn't apply. The rebate it would offer is covered by the Item of Power discount. 

Trying for a more complete write-up than I'd posted earlier.

The Slender Man

From a distance, the figure appears to be a tall, thin man in a black suit, standing near the forest's treeline.  As you grow closer, though, a sense of wrongness falls about him.  His apparent height stretches to well over 9 feet tall.  Rather than human arms, he sports branching tentacles.  It's not until you see his inhuman face, however, that you realize the true terror before you.

High Concept: Mysterious Apparition
Other aspects: Fond of Children, Twister of Minds, The Operator Symbol Ⓧ, Found You Forever, Symptoms of his Presence, Persistent Silence and Outstretched Arms 

[-4] Supernatural Recovery
[+0] The Catch is unknown (and possibly nonexistant)
[-8] Physical Immunity
[+0] The Stacked Catch is also unknown
[-2] Undying (much like Living Dead's Death Is A Nuisance power, no Taken Out result of death against the Slender Man truly lasts.  He might be incapacitated or banished for some time, but he will always return to the world, sooner or later.
[-4] Supernatural Speed
[-4] Supernatural Strength
[-6] Incite Potent, Lasting Terror, Obsession, and Madness At Range
[-4] Mastered Domination
[-1] Cloak of Shadows
[-0] Human Guise
[-1] Claws
[-4] Long Grasp: The Slender Man may use most, if not all, of the Trappings of the Fists and Might skills from an adjacent zone.  This includes ranged attacks and grapples.  In addition, the Slender man may perform spray attacks unarmed using those skills.  This means that if there are multiple opponents in the field who possess aspects which may be invoked to initiate a grapple, The Slender Man may attempt to grapple all such opponents with the same action.
[-1] Mana Static
[-2] Swift Transition

Total Refresh cost: -41

Skills:
Fantastic: Intimidation, Deceit, Presence
Superb: Fists, Athletics, Discipline
Great: Empathy, Alertness, Might
Good: Endurance, Conviction, Lore

Other physical skills default to fair, non-physical skills to average

A veritable nightmare.  Weapon: 6 Physical attacks at Superb from up to a zone away, ranged zone-wide grapples, immunity with a catch to be decided by the GM, if any (options could be holy items, his own substance, or more esoteric mystical options) with recovery that's potentially Catchless, and the power to truly break the mind of his chosen prey.   He often surrounds himself with Enthralled slaves or Renfield-esque servitors.  Physical combat would be a slaughter, and should last only long enough to show that the players should run without his Catch.  Actually killing the Slender Man is impossible, but it may be possible for players to defeat the Dresdenverse version in a couple ways.  Discovering and using the Slender Man's Catch against him (if one exists) could allow players to drive him away, or characters might find and perform a magical ritual to ward him away or bind him. This should never be cheap or easy; perhaps the ritual is in a book of Outsider lore held in a Venatori enclave or the like.

Modifications:  If this version of the Slender Man is too extreme for your tastes, you can lower the Strength and Recovery to Inhuman, or eliminate the Strength and Claws entirely - just make sure you don't remove *all* his teeth.  Y'know, if he has teeth.  If (god forbid) you wish to make him even tougher, you could boost Strength, Speed, and Recovery to Mythic - though by that point, he's even further into "plot device" territory than he started.  In fact, if the party doesn't have the Slender Man's Catch, he could (and possibly should) be run as a Plot Device in any physical combat.  You go up against him directly without that sort of leverage?  You're dead.

A broad class of being, called Memnovores, much as fear-eaters are called Phobophages.

While those are all, to some extent, considered virtues by Christianity, they aren't really defining virtues like Faith, Hope, and Love.  Something big enough to have a Sword should be one of the primary virtues of the religion, IMO.  That's why I suggested Grace, which is at the center of the Christian conceptual worldview.