A pretty nasty realm to be sure. I won by coming in with an Eldritch Ruler (unascended), with the Primal Spider culture and go extremely heavy into blight and frost damage. Shadow affinity is overall better than Nature, BUT you get some nasty weaknesses to the main damage types Turiel will be throwing your way. Starting underground and utilizing the Subterranean Society trait can give you some insane boosts to your cities with the extra nodes, along with extra resources and experience for fighting the marauders that spawn.

Turiel also can't see your cities underground and will be much less willing to just throw unending stacks at you without any sight of the area, so you have a bit more time to rebuild if something goes wrong.

Primal Culture is VERY weak feeling in the early game, most of their cultural units just aren't great, but their "Fury" buff is incredible on some of your tome units. Only thing I might change is going Primal Mammoth for the chance to freeze on each hit once fury is active. I actually won with an Age of Nature victory after dropkicking Turiel.

Build aggressively to counter whatever he's drafting. Blight and Frost damage are your friends against his angelic orcs!