I'm working this one out, based on Bayonetta. There would be a parallel form for Lumen Sages, as well, though there may be a few changes in between the two. I'm not sure of the power level though.
Umbran MagicDescription: Being bound to a demonic power of Inferno, the Umbra Witch is capable of summoning demons and slowing subjective time in combat
Agenda: Destroy the angels of Paradiso (up to the GM if this means the actual angels of the Dresdenverse or a separate form of Nevernever spirit, akin to the difference between a Fallen and the frog demon).
Evocation: Umbra Witches are able to use Chronomancy to a limited extent; they cannot travel through time, but are able to slow it down when threatened. They also are able to use their Hair as an element of magic, akin to Air or Spirit in function.
Thaumaturgy: Demon Summoning
Evothaum: Umbra Witches can use summoning magic and alchemy with the speed and methods of evocation (for the latter, this still requires ingredients and appropriate recipes).
Extra Benefits: Any suggestions or alterations welcome!