If a dogpile can't slay a god what what can? Simple, the Godslayer.
If Auric has regained his divinity it makes since that he would also regain the true immortality of a god, of the same type as the immortality of Os-Gabella or Nemed. He need not be tougher than mithril, as he would instantly heal from any wound and thus no injury would last more than the briefest moment. A million trained soldiers would be no more useful than one, as he would be fully healed as soon as any blade that scratches him is pulled out (or maybe pushed out by the healing process), unless said blade is The Godslayer.
I don't think that ships should be very useful against Auric Ascended, as thematically the water near him would freeze sold. It might be nice to have Snowfall_greater transform even water to Snow, and to be done passively wherever he goes.
Of course, he should never be able to survive the encounter with any unit with the Godslayer. I'm thinking the Godslayer should also let units move though impassible terrain, so Auric can't hide in the mountains.
There is no point in having Auric Ascended have 2 versions of Snowfall. If I were to give him another spell I'd let him summon Frost Giants (which would be like Wilboman minus the Hero promotion), perhaps creating them in python so they are permanent and not limited in number.
I think that Avatar should grant Fear, healing while moving, 100% healing after every battle, and Blitz.
I also think that Auric Ascended should have to be upgraded from the normal Auric Unit, and keep any promotions that the Mortal Auric purchased but never be able to purchase any more once he fully exemplifies Stasis. Having Auric fight a lot and get a lot of promotions would make Auric Ascended much stronger, but loosing him before he can ascend would make the ascension impossible and cost you your traits.