Cool power, sounds like an interesting premise to a character!

I'd peg it as Supernatural Sense [-1] myself, as it's very limited.

Long time lurker here, first time poster in this thread :-).  You guys got me addicted to Worm about a month ago, and just in time for it to end! ;_;  Fantastic job detailing the characters, I've enjoyed all the conversions.

Between this thread and the PBP Recruitment one I was intrigued about converting Worm over to the DFRPG.  I didn't want to derail the topic of this thread (actually statting out the characters vs working on base rules for running a campaign in the 'verse) so I started my own thread:

http://www.jimbutcheronline.com/bb/index.php/topic,39553.msg1946061.html#msg1946061

 I hope you all chime in with your thoughts/opinions, thanks!

Heavily WIP.

Powers:
"Mover, Shaker,
   Brute and Breaker.
Master, Tinker,
   Blaster and Thinker,
Striker, Changer,
   Trump and Stranger."

Many of the most common powers in Worm have Trade-Offs, Limitations and Variable Powers built in (see above).  Everyone seems to have something unique about their power.

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Mover:
Flight, Supernatural or Mythic Speed, Teleportation.
Ex: Velocity has Supernatural Speed tied to Trade-Off.  He gets more accurate punches but doesn't deal as much damage.
Oni Lee has Teleportation with Additional Effect, tied to a power that creates his clones (Incite Defensive Effect, perhaps?).

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Shaker
Modified Demesne Power, allows aspects to be placed on the terrain via Declaration, attacks, defense, blocks, and borders as upgrades.

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Brute
Supernatural/Mythic versions of Strength/Toughness/Recovery, some variants of Physical Immunity.  Often times The Catch for such a power will be Power Nullifcation for a simple [-0].

Ex: Weld probably has Supernatural Toughness and at least Inhuman Strength and Recovery.
Alexandria is probably a munchkin with Mythic Toughness + Undying (the Catch: Strangulation) along with Supernatural Strength, Speed, and a boat load of other powers.

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Breaker: A hodgepodged category of powers (along with Trump).  Often self-transformation abilities that don’t drastically change one’s own form.
    Size Abilities, Amorphous Form, etc...

Ex: Fenja/Menja have Gargantuan Size (Hulking Size's big brother) with the ability to turn it On/Off.

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Master:  Whole big rules subset, WIP.  The following are just my notes:


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Tinker: Tinkers have a version of Thaumaturgy focused on Crafting.  It uses Scholarship/Capes for control/complexity and they often have lots of enchanted items.  Refresh spent on Refinement for Specialization or extra item slots is common.  Power suits or a signature device/weapon are often Items of Power.  Often, someone else can use a Tinker's device even if it's not made for that with a good Scholarship roll (= to the complexity of the device).

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Blaster: Incite Effect, often with Power Immunity.  Oftentimes Blasters will have Trade-Offs and other small powers (Super Senses and the like).

Ex: Legend has Incite Effect with Trade-Off/Choice and Super Senses for his superior sight along with Flight and some Inhuman abilities.

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Thinkers: Thinkers probably use a re-skinned Guide My Hand ability as a base, substituting Mental Stress for FP's to use their abilities.  Particular Thinkers will take Inexplicable Knowledge (the wiki), a re-skinned Sacred Guardian (DFRPG:OW from Mouse), "5 seconds ahead" (DFRPG:OW from Abby) Skilled, Jack of All Trades, and Modular Abilities (for Stunts).

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Striker: See Blaster, but short-ranged!  A lot of Natural Weapon (wiki) powers fall here as well.  Some powers use Fists over Conviction/Discipline.

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Changer: WIP

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Trump: There's a large variety of abilities under this category.  Often times these powers will affect other capes/powers.

Grant Power to Others [-2] - (Can’t grant self [-0]).  Range by touch (default).
    [-X] Common Limit - Duration
    [+X] Increased targets (use progression table)

Power Nullification [-X] - Similar to counterspelling rules, often with Power Specialization to get that edge in.
   [-X] Common Limit - Range
   [+X] Area

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Stranger: Powers allow the cape to use Stealth in more tangible defensive ways.  Characters with Super Senses should get a bonus to Alertness rolls vs. Strangers = to the Refresh they spent on their ability.

[-1]: Allows you to make Stealth check without needing concealment (Invisibility)
OR
[-1]: Blocks on yourself vs. Alertness ().  Doesn’t affect area attacks (?  Similar to Incite Defensive Effect).

Add-Ons:
[-1]: Can attack and ‘restealth’ as a supplemental action.
[-1]: When you stealth, others forget you if they fail an Alertness check.
[-1]: Ignores even Supernatural Senses (they don't get the standard bonus)

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Next: Character Archetypes

Thanks for the replies everyone!  The reason I wanted to stat up a Crossroads Demon is because one will interact with a PC soon.  I wanted stats mainly so I could run a social encounter between the two.  I doubt the PC will want to strike a soul trading deal at first, but I'm sure a few NPCs will over the course of the campaign.

I figure if the PC somehow wins the conflict (which should be incredibly hard), they can get a decent deal from the Demon - information or a useful trinket at the cost of some debt but without their soul on the line.  That said, if I can semi-accurately model Crossroads Demons with DFRPG stats I'd be pretty stoked!  Here's my shot, after reading your advice, researching some, and a bit o' brainstorming:

Crossroads Demon
High Concept: Demonic Genie
Aspects: Devil with the Details / An Offer That Can’t Be Refused / Sweet Lies & Half-Truths / Crossroads Contract

Skills
Superb (+5): Deceit, Empathy
Great (+4): Presence, Rapport, Resources
Good (+3): Conviction, Intimidation, Lore
Fair (+2): Alertness, Athletics, Discipline
Average (+1): Endurance, Fists, Might

Stunts
Honest Lies (Deceit)
Paragon of Sin (Conviction), as per Tower of Faith
Read the Surface (Empathy)

Powers
Crossroads Contract (Item of Power) [-0]
Sponsor (The Crossroads)*
Sponsored Magic (The Crossroads) [-4]
Supernatural Toughness [-4]
   The Catch [+3] - Holy Objects and the like. (+1 for Rarity/+2 because it's well known)
Swift Transition [-2]

Items
Focii: Varies - This may be a quill, ruby red lipstick or similar (+2 Control/+1 Complexity to Wish Granting spells).
1 Enchanted Item (Power 3, Ex: Love Potion that applies 'Lust' aspect to a target)

Refresh: 0 (10-10)

Stress
Physical OOO(OOOO), Armor 2 / Mental OOOO, Armor 1 / Social OOOO, Armor 1

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Sponsored Magic (the Crossroads):
In the Supernatural universe, the wish granting that Crossroads Demons do is a matter of spellcasting, instead of an innate ability, which limits what they can do**.  Crossroads Magic mainly centers around Thaumaturgy (Mostly Entropy and Wish Granting), sometimes done at Evocation speed.
Extra Benefits: See Below

Crossroads Contract (Item of Power) [-0]
It is What It Is [-0]: A metaphysical contract between a Crossroads Demon and the oathgiver.
Unbreakable [-0]: Only a Crossroads Demon or its boss can destroy a Contract.
One-Time Discount [+0]: Having no physical form to interact with, it offers no discount.
Sponsor (The Crossroads) [-0]: As per the power, but it may only be used to fulfill the bargain*

*http://dfrpg-resources.wikispaces.com/Sponsor
**http://supernatural.wikia.com/wiki/Crossroad_Demon

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With these stats, a Crossroads Demon has a variety of options to fulfill their client's needs.  For a client who wants money or an object, the Crossroads Demon can make a Resources roll (at +4, plus some additional aspect Tags via Sponsorship to get what they need).  If they want a task done, either acting on the client's behalf (murdering someone with magic) or providing an Enchanted Item (like a Potion of Love) might suffice.

For those who wants a little more, a Contract might be what they need - as it is an Item of Power the character is required to change/add an Aspect representing the deal which seems appropriate. For instance, if the client wanted to play Guitar better, they take the contract, add 'Bargain - Demonic Guitar Skills' and can now use their new Sponsor ship to take a debt and get a free tag on Performance rolls.  Suddenly, they're a whole step more talented - if they were at +2/+3 (journeyman or professional capacity) they're now +4/+5 (veteran or masterful capacity) or if sent above that, they're now skirting the boundaries of human capacity.

Now, if the client wants something fantastic, like powers - that can be done via Sponsored Magic.  As an Extra Benefit of the power, a Crossroads Demon can cast a spell akin to a Wizard's Deathcurse, using the willling client's life force to fuel the spell.  The client doesn't pay the usual price of death instantly, but exactly 1 year later at which point the Demon will come collecting.

Besides that, the Stunts are there to make social encounters with them tough, unfair even (with Paragon of Sin, I imagine they recite to themselves some sort of Infernal Salesman Creed instead of a prayer).  They should be able to have an idea of what their client wants and how desperately they want it (Read the Surface).  And any time they can a Crossroads Demon should fulfill their end of the bargain with as little heavy lifting as possible (Honest Lies).

Supernatural Toughness is just a standard demon power, but Swift Transition is especially useful for just avoiding combat altogether (as long as they're caught in a Devil's Trap or similar!)

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Well, that's my best shot for now!  Comments, critiques, and suggestions are welcome.  I'm sure a lot of fine-tuning can be done here :-)

Channeling (Biomancy) seems like a legitimate choice to me, the elements presented in the book are simply the Classic Elements that most North American/Western European wizards use.  Some Asian Wizards (like Ancient Mai) most likely consider Wood and Metal to be separate elements.  There might not even be a need to upgrade to Evocation if this fits all the character wants to do.

Those effects seem just fine to me, they're really just all descriptors :-).  Some of the character's spells will probably be Discipline vs. Endurance instead of Athletics like most physical evocations. 

I have a Blood Sorcerer BBEG in my game who uses Biomancy.  They might not fit your player's character, but here's some of her Rote spells:

'Thousand Cuts’ Type: Biomancy Maneuver / Power (6+): ‘Bloodied’ sticky Aspect
   Control: Endurance (+3) or higher avoids / Target: All targets seen in 1 zone
   Duration: One Action / Opposed By: Target’s Endurance skill, magical blocks

‘Exsanguinate’ Type: Biomancy Evocation / Power (6+): 6 Shifts (+1 if ‘Bloodied’) [Because of her Blood Drinker power]
   Control: Discipline to Attack / Target: Target in sight
   Duration: One action / Opposed By: Target’s Endurance skill, magical blocks
   Notes: Caster can use this to fulfill their Blood Drinker ‘Taste of Death’ ability if they kill their target.
- Meant to be a 1 -> 2 Combo with the first spell.

‘Immortality’ Type: Biomancy Block / Power (9): Block Strength 7
   Control: N/A (Tag + Incurs 1 Debt) / Target: Self / Duration: 3 Exchanges
- With this rote active, anytime the caster is hit their body mends the wound immediately - unless the attack is greater than 7.

To my understanding, a player can Maneuever someone 'Prone' but it won't stop them from moving by itself - that's definitely a Block action.

That player can tag 'Prone' in rolls where it makes sense (like attacking them) - if the aspect is fragile it'll just fall off but if it's sticky you can continue to tag it for the duration.  But if they want their maneuver to keep their enemy on the ground they have to attempt to Compel them (at the cost of 1 Fate point), but if their opponent pays one back they can take actions like moving with no extra hassle.  If they end up moving and the player cared for accuracy they may want to change the wording of the placed aspect to 'Dazed' or 'Off Balance' or similar.

The book gives a similar example with 'Blinding' on page 208.  All it does is create an aspect that can be tagged, if the player wants it to do more they can compel what they want to happen, with the GM's/group's permission (more on pg. 107).