I mean WOJ is Erlking rose as part of a ritual reminiscent of the Darkhallow, presumably less necromancy though.

"If he'd succeeded, he'd have had the collective power of all of those supernatural beings and then some.  He'd have been clearly stronger than the Ladies, and a full-on equal to Mab.  I mean, why do you think the Erlking was summoned as part of that ritual?  Because that's how the big E got so boss in the first place. 
For that matter, how do you think the Mothers and Queens and Ladies established their original base of power?  That big old sacrificial, power-sucking stone table in Tir na noth isn't there for its primitive decorative aesthetic."

And this tidbit

Actually, in the Dresden universe, the Wild Hunt can be led by a number of beings--INCLUDING Cern, but not exclusive to him.    The Erlking (who isn't Cern) is a being of Faerie who is in Mab's weight division, if not her equal.  I believe he is identified as the ruler of the goblins--which should not necessarily be equated with Tolkeinesque/Gygaxesque goblins

Looking at the Lore of the Wild Hunt it's an honour as well as a curse everyone from Kin Arthur Pendragon to Sir Francis Drake wee said to be a part of it. Theirs even an infamous dodgy socttish lawyer somewhere. I'm not quite sure if it fits with Dresden Files Fae heavy interpretation of it, but the Wild Hunt was full of the most dangerous spirits of voilence and leadership.

 In some versions they even have hounds from hell or Heckhounds as they're known in Dresdenverse. But their point was too hunt down the demons and escaped souls from Hell, usually on times when the barrier between spirit world and real world are at it's weakest. The Equinoxes or Samahin, All Hallows eve etc.

So if using the folklore surrounding it Erlking is the stable Leader of the Wild Hunt when all the other leaders tend to rotate in and out. He keeps them more or less undercontrol for the rest of the year and unleashes them once or twice a year at most.

https://en.wikipedia.org/wiki/Wild_Hunt

Drakul vs Vadderung

Honestly I expect Marcone drew up a contract with adendums and failsafes similar to what Butters did with Bob.

Goodman Grey vs Kincaid over rival contracts.

I mean what confuses me is Wizards live for 300 to 400 years but Ebenezars only had one child?

That's more sterile than the White Courts supposed to be.

I mean tbf some powerful beings tend to be obtuse about things that aren't in their purview. Erlking needed Kringle to translate during Cold Days and was confused by Margaret le Fey's necklace and didn't make the connection of Dresden being her son.

The svartalves have an almost autistic social interactions.

Even Mab struggles to keep up with the pop culture references, and thats with her daughter playing interpreter.

Oh right I forgot to add this.

I really really want Harry to come up with a strategy for huge enemies, beyond trying to trip them, or relying on the fact they can't bank or turn and leading them into a trap.