Usually I try to avoid introducing celestials in my campaings, especially angels. To my mind, heavens should remain mysterious and silent. There were one exception though, when I used Ghaele as major NPC.
Due to thorough web searching I was able to find almost all clarifications concerning Shadow Magic I needed except for just one: I still don't know for sure how long Umbral Touch's slow effect lasts. So I'd be very grateful if someone (perhaps even Ari if he is not too busy now) clarified this...