You could always do Spirit Maneuvers to place aspects on you that you'd de a free invoke on, such as "Claws of flame", if you had an awe-full lot of mojo you would get to double stacking aspects like "Frost glazed Hand" and "Spirit chanrged Arm"  etc.  Also using ritual effects to change yourself adding claws or other supernatural creature features including strength, speed, etc. are in the rules. 

Ideas for a fire base defense:

• wall/sphere/shield of fire that consumes all that comes at you
• Smoke and shadows to conceal & distract, kind of like a veil defense against awareness
• small fiery demons/spirits that swirl about meeting each incoming attack with distruction
• Haze about your body that lites up with fire when attacked to consume its force (more of an armor idea than shield)
• Heat wave shimmer that distorts thing away from you

Fire is big on the consumption and refinement, so consume/redirect the attacks energy to fire, could also give you some interesting way to say you are consuming the attacker energy and throwing back at them

hope that helps

Probably something like this, based more of a sponsored magic and a few powers than strait wizardry. 

Aspects:
 Skinwalker, former Messenger of the Gods
Most Disturbing Thing you will ever see
Old as Time
Relishes in Destruction

all relevant fighting/magic/disguise skills Superb or better

-4 True Shapeshifer
-2 Mimic Form redundant
-3 Incite Emotion (Fear/Despair?, at Range, Potent)
-20 (or maybe more?) Modular Abilities
-w/ Supernatural (or possibly Mythic) Speed/Toughness/Strength/Recover
   probably a +0 catch unless there is something we don't know about it
-2 Glamor redundant
-4 Sponsored Magic (Divine Power of old Navajo gods)
-5 Refinement

Refresh -36 (at least)

I don't think I am leaving anything out, thats one frightening beastie, I feel sorry for harry all over again, but really something like this is more of a plot device than a stated threat