As posted above, there are ways in which characters who start out as pure mortals can gain magical power:
From the books:
- Become an Emissary of Power (one of the Knights, Winter/Summer mantle, etc)
- Pick up a Denarian Coin (or other such items).
- Infected Red-Court Vampire.
- Become a "True Believer" (for any god or Adversary).
- Someone gives you hexunwulf pelt. You need to roll against conviction not to turn evil every time you use it or something.
Other powers:
- Barter for power with entity/ritual.
- Someone gives you a Noose.
- Dragon Emissary. Become a Monoc employee (good health plan).
- Find Bob on a shelf in a curio shop.
Not-quite-human possibilities (mainly works for younger characters):
- White Court but never knew it (hadn't killed anyone during sex yet).
- Changeling but never knew it.
- Scion but never knew it.
- Latent wizard powers:
Molly only became a wizard around 18, and she has Council-level powers. A minor talent might only manifest itself later on.
Billy and the Alphas only became shapeshifters in college, and had to be taught by Tara.
Shadowman in first book only found real magic later on in life.
Weirder:
- Involuntary body switch with necromancer into a wizard body (not sure what the rules are on that one).
- Involuntary shapeshift into more powerful body (ghoul)?
- Bob the skull takes over your body (maybe only partially). He has the power to cast spells.
- Get killed. Come back as ghost/zombie/undead/force ghost with free will.
- Accidentally stand in middle of a vortex at during a DarkHallow.
- Your mother just died. Turns out she was the Archive.
Finally:
Get Cursed by a Saint to become a Loup-Garou.
Edit: Or maybe you are a relative of Macfinn. The curse is that there would always be someone in the family who was afflicted. Macfinn just died...