Ahh yes that is true. My mistake for misinterpreting the theory. Yes, as a character arc it still would work despite the plot. Thank you for the Jotunheim theory, I will get into that in a moment. As for Muspelheim...I too have wondered if it might be Outside. If it is, then Loki could be part Outsider demon, if not completely, especially as in some versions he was from Muspel, not Jotunheim. If Loki were from Muspelheim, and Odin met him, then Odin may have crossed Outside. I know the more accepted version is that Loki is merely a Jotun...but I feel that's a bit boring for Jim. Also if Muspelheim is Outside, then where is Surt? The EPIC guardian of Muspelheim who will burn all the Nine Realms in Ragnarok with his sword of flame. He is the Destroyer, similar to Kali or Shiva in Hinduism or Apophis/Apep in Egyptian Mythology. Not that I am saying Hinduism is mythology, for the record.

The divide between the Faerie Courts coincided with the Fae assuming the defense of the Outer Gates, and also with the decline of paganism in Scandinavia. Previously, the Jotun had guarded the Outer Gates, and the Aesir had protected Midgard from the Jotun. However, with the decline of pagan worship, Odin, the Normans' chief god struck a deal with the Fairy Queens¹, the Celts' chief goddesses, to ensure the defense of Reality.

That all works quite well I think. Though this raises a few questions: why were the Aesir and Jotun's guarding all of reality? Did anyone guard it before them? If so, who? Was it the Greco-Roman Gods? The Hindu Gods? All the various Gods? My personal belief is that perhaps the Angels were the original guards, and that the various Gods and Goddesses of the many pantheons were either created by the angels OR were former angels OR were helping since the beginning too. The angels can no longer guard the gates as they had to fight an enormous civil war that they are sort of still fighting against Hell. I suspect all of the pantheons guarded the gates at one point...the way the WOJ is worded makes it sound like they have been fighting since the beginning, everyone else has left.

Per Bob, Hecate was originally a Hag who achieved divinity through a bloody ascension rite.² Mythologically, she's one of those weird pre-Olympian mystery goddesses infesting Greco-Roman paganism. The tri-part goddess statues in Hades' Vault³ lead us to conclude that the three Fairy Queen mantles are, together, Hecate in her triple goddess form (Mother, Maiden, Crone). Given the confusion in the real world over whether Hecate is the Crone or the trinity, I'd say it's fair to assume that she is both. At some point after her ascension, she spun off her power into the three mantles, and kept the Crone mantle for herself.

It is currently unknown to whom Hecate the Crone gave the other two mantles to, and I know I've shed pixels trying to pick Olympian divinities who could take the mantles. This makes no sense, however, as the Olympians have their own divinity, and would not need to accept more power from Hecate the Crone. Given the connection apparent between Hecate and the Fae, we must look elsewhere in Europe.

I think your conclusion may be false with Hecate. Yes, the triple-goddess statue in Hades vault COULD be Hecate, but I don't think that's the whole tale. Harry identifies the statues as the Lady, the Queen and the Mother of Summer and Winter respectively. And he's met them! Now we know they have other names/identities. I think Hannah Ascher either identified them incorrectly OR she was only partially right. I think over recent WOJs and via lines in the books it's been made clear that gods are nowhere NEAR as powerful as the Mothers and Archangels. Therefore I just don't think Hecate can be Mother Winter. Not to spoil to much potentially, but I suggest anyone who wants to get a more precise version of what Hecate/the Fates/Norns/Queens/Triple Goddess might be should read Neil Gaimen's Sandman comics. I suspect Jim might have got some influence there. I think his Power scale might also be similar to, in relation to where gods, angels, archangels etc stand.

Also, why would suddenly Hecate, a pre-Olympian Greek Goddess (a Titan in some versions) go to the Faeries of Ireland and Britain? She hasn't been linked to them afaik outside of something like the Sandman. It seems really odd, the connection between the Fae and the Olympians in the Dresdenverse. I suspect we don't have the full puzzle.

they are the Celtic pantheon, but Christianity sapped their power, spinning them into heroes with supernatural powers instead of gods. I speculate that the Crone Hecate found her Mother and Maiden within this pantheon of not-quite divine figures. By binding the Mother, Maiden, Crone to the existing Tuatha De Danann, the Fairy Court arose from the Mantle-wearers and their followers.

I think you are definitely onto something here, it certainly fits your theory. However, we have no actual facts from Jim or the books that this might have or even could happen, so it's a wait-and-see scenario. Certainly a good reason why some old gods losing power might suddenly accept Power from Hecate. Though mind you, Hecate's power would be drained as well, she wasn't really being worshiped too heavily around that time. She might have kept getting more power, or found alternative sources to belief. I also find it interesting that Hades is still quite powerful, even without belief. That being said, Hades did say he no longer has the power to influence destiny or something to that effect.

All your stuff on Jotunheim and defending the Outer Gates works. Definitely some some interesting links between Winter and Jotunheim. The Aesir, while not being exactly happy go lucky guys, did live in a bright realm in the sky with elves next door and OLD PAGAN GODS (VANIR) on the other side. Very Summer-y. Somehow the Vanir angle seems to be important to me, though I haven't really got a good theory why...

1066 is where this all comes together. The Norse Normans invade Celtic England even as Norse paganism is on the decline, and Christianity on the rise, in Scandinavia. The decline of paganism is a problem for the Aesir, as they aren't worshiped as much as in the past, and are losing power. This is not a problem for the Jotun, as they aren't worshiped as such in the first place. The invasion of England is a problem for the Fairy Court, as the people who tell their stories are getting slaughtered.

So Odin, chief god of the Normans, and the Fairy Queens, representatives of the English, meet to discuss terms. This is a blending of the various sources for British fantasy, the Norse, Celtic, and Greco-Roman religions. The end result is that the Jotun are banished (to team up with the Fomor), the Normans take England, and the Fairy Court splits to assume the defense of the Outer Gates. Hecate the Crone assumes the Mother Winter role. And she loses her walking stick.

Mab and Titania

My gut says that Mab was the Maiden at the time of the split. Then, during the split, the Crone Hecate became Mother Winter, The Maiden Mab promoted herself to Winter Queen, and the Mother became Summer Queen. For symmetry, Mab's twin sister, Titania, became the Summer Lady (where Mab started). When Mother Summer abdicated (I'm still going to guess this was Baba Yaga), the Summer Queen became Mother Summer, and Titania became Summer Queen.

Well this all seems to work together. I think Odin was invading for a reason, attempting to force things with the Tuatha de Danaan. I think he lost and the terms were made to him, not the other way round. You forget that the Vikings led by Harald Hardrada lost to Harald Tostig. William's Normans beat him after that. MAYBE Odin was pulling the strings and won with two armies. That does seem to be his style. But that was the last Scandinavian invasion of England, so I think he lost something there. And Odin even says he isn't what he used to be. He's like a soldier who has gone into private security because he is out of the front lines of the war (reasonably common actually).

Now I don't get on board with Hecate becoming Mother Winter and all that. WOJ actually says the Mother Winter is Baba Yaga...I certainly don't think she lost her staff in 1066. I think that was later, to the White Council, after the original Merlin.
I also think no one has considered that the Mantles predate the Courts of Faerie. I think that they are REQUIRED for whichever pantheon is holding the Outer Gates, in order to keep the Outsiders Out. Seems like they are tied into every mythological pantheon, everyone has their oen names for them. Norse call them Norns, Greeks call them Fates (Moirai), Baba Yaga in Russian, Hecate pre-Greek etc. Probably Jim could link them everywhere if he chose too.

Wow, long post. Did not intend it to be this massive...woops! Sorry to rip on your arguments, I am mostly just stirring the pot and seeing what happens. I really did enjoy the theories though, they have been some of the most compelling I've seen here on the forums.