I found my first Skin of the Vipermagi during my playthrough with Wizendraw, my Holy Freeze bow paladin, in Nightmare, Durance of Hate level 2.

I had 99% magic find. It rolled perfect (13) on the Magic damage reduced 9-13 and a respectable 32 (20-35) on the All resistances. I added a perfect topaz for 24% magic find.