Sarissa comes from an old Hebrew word, which is the same word that Sarah derives from (and in fact, Harry accidentally calls Sarissa Sarah when he's trying to remember her name.) The brilliance? The same word is also the Hebrew word for "princess." As in, "Daughter of a queen."
Sarissa's actions at Harry's birthday party: Of course the only Changeling brave/confident enough to bring iron into Arctis Tor is Mab's daughter.
Two of Mother Winter's names are Skuld (a Norn) and Atropos, one of the three sisters. It is also stated that there is a name that both the Mothers share that is even more powerful. Given the domains of the first two names, the third is most likely Fate. When you realize that in the original myths the creatures of Winter and Summer are not different individuals on opposite sides, but the same person at different times much like Kringle and Odin, the Mothers' conversation makes a bit more sense, kind of a "what once was split be made whole" kinda thing.
Going into Horror, when one thinks about what if Harry had used Fates' name. It's a good chance that instead of one of the Mothers he would have gotten the one and only Mother. Honestly, if Mother Winter is Fate, then the idea that Mother Summer is also Mother Earth makes a lot of sense.
Kringle is the expert on temporal manipulation. Which makes sense when you think that Santa would need a lot more time than one night to get all around the world.
Kringle riding with The Wild Hunt makes a lot more sense if you know that he's Odin, who commands the Hunt in mythology.
YMMV on whether this is brilliance or horror. Kringle is Odin, which means that the face of Christmas, the largest Christian holiday, is a pagan god (though Kringle admits "Santa Claus" is both recent and primarily secular). It also works in the real world as Odin is a candidate for the original myth of Santa Claus.
Erlking and Kringle are anagrams of one another.
Going off the anagram mention, it stands to reason that when Kringle took the "Santa Clause"-Mask, Erlking took the "Krampus"-mask and went after naughty children.
On Odin's source of power. Backup shows that a lot of the beings in the Dresdenverse depend on belief (or at least a large number of people knowing about the being in question), almost certainly including gods of various calibre. Since the worship of Odin is not nearly as big now as it was in the Viking heyday, how does he have all the juice to fight vampire gods and raise Norse heroes from the dead? Who believes in Father Christmas? Which might explain why the Erlking has a reputation for being a protector of children, despite his ferocity. He's been looking out for his hunting-buddy's best interests!
With respect to Proven Guilty. At the time, it appeared that Molly was taken to Arctis Tor as punishment for interfering with Winter's plans. But this was also when Molly was most likely to be executed by the White Council. She was kidnapped so that she would survive long enough for Dresden to become her protector. And Dresden became aware of her potential as a result of being told about black magic by ... The Gatekeeper. Who it turns out shares defense duty with Winter at the Outer Gates.
Alternatively, remember how "all of Winter" was after Harry in Proven Guilty? Now consider that most of those faeries were supposed to be guarding the Outer Gates. Also remember that this was at least partly Maeve's idea - and she was already saying that Mab was insane and therefore must have already been infected by Nemesis. And then Michael mentions there were Outsiders involved in the Red Court attack on the Warden training camp. It looks like the entire thing - Molly's kidnapping, the rescue mission, everything - was a diversion orchestrated by Maeve to get Outsiders into reality.Nice Job Breaking It, Hero.
Both Mab and Harry spend the book having daughter issues. Specifically, having a daughter that they, in their own ways, love and want to help, but because of duty can't either be with (Maeve) or help (Sarissa). It ends badly for Mab. One dies, and the other is taken by Summer forever. A possible foreshadowing of Harry's own relationship with Maggie?
A meta one: Butcher gives the weight that Dresden can press in both kilos and stones. The European fanbase approves, because we get length in feet and inches often enough to know what it is in meters - but weights are something completely different. This way, everybody understands just how ridiculously strong Dresden has become.
So how did thousands of Eldritch Abominations get trapped in Demonreach? Well, that's what the giant uber-circle and the Warden are for. The Warden summons some unspeakable horror inside of the perfect, unbreakable trap and lets the island clap it in irons for him.
Waaaay back in Storm Front, Harry encounters a Three-Eye junkie at the police station, who raves about how "those who walk before and He Who Walks Behind" are coming for the wizard. At the time, Harry's floored that the addict could See the mark of the Walker he'd confronted as a teenager on him. But now, it seems the junkie might actually have Seen Harry's future as well, because "those who walk before" might actually have been a reference to Sharkface — aka He Who Walks Before — and his power of Self-Duplication. Sells' potion/drugs may have been more potent than Harry ever suspected.
On a meta level, the reason Molly was able to become the Winter Lady conforms perfectly with Winter philosophy. During Changes, both she and Harry suffered trauma from killing the person they loved. The difference is that Harry could not bear the pain of this (and killed himself) where Molly endured her guilt and survived, making it possible for Lea to train her. In a culture that values strength highly, it makes sense that she would be ranked higher than him.
According to Word of God, Justin Du Morne was collecting the Starborn to raise them into a weapon to destroy Outsiders. So... does that mean Ellaine Mallory is also a Starborn Outsider-killer?
At the end, Mab tries to make the events of the climax less horrific to Harry by explaining that she had intended for Molly to become the Summer Lady, but things didn't quite work out. But considering Titania's reaction to meeting with Harry, and Lily's more especially, and knowing what we know about Molly's character, isn't it even creepier to think of her being considered as the prime candidate for a position whose job description literally includes poor emotional control? Possible Fridge Brilliance: perhaps that is whyMab considered Molly a better fit for Summer. Mitigating this would be the fact Mab didn't intend for it, but merely knew it was a high chance of happening and had several plans in motion. Note, had Harry just summoned Mab when he arrived inside the circle, things could have happened differently.
Blink and you'll miss it, but Harry mentions four "famous" historical figures that had held the mantle of the Winter Knight before Lloyd Slate: Gilles de Rais, Fritz Haarmann, John Haigh, and Andrei Chikatilo. All of them were executed as serial killers, and three of those four were known to prey on children. Given the similarities in those cases, and the repeated statements from various parties that the Winter Knight's mantle alters its holder's personality to conform to its archetype ... it's tough to blame Sarissa, or Fix, or Harry's friends, or Harry himself for being scared.
Throughout the novel, Harry takes great pains to try to keep his friends and family out of the brewing conflict with the Sidhe, since involvement in his affairs makes anyone fair game. He utterly fails. Everyone's involvement is known — Butters, Andi, Mac, and Justine all catch hits for it despite being only briefly involved with supporting him. Those people? Got off light. Thomas was an active fighter in the whole affair, and Molly is now Winter Lady. They can at least take care of themselves on some level, though. Karrin killed Maeve, Mab's daughter, by shooting her in the face. Worse, the person likeliest to take revenge isn't Mab — it's Redcap, Maeve's lieutenant and the fairy equivalent of a Serial Killer.
Harry spends the entire novel lacking the nerve to visit his daughter, and never works himself up to where he dares go to the Carpenters' place and come inside. He's afraid she might remember the events at Chichen Itza, and how he'd killed Susan on the Red King's sacrificial altar. By the end of the novel, Harry has just started to embrace the notion that he needs to re-integrate with his friends again, a process which one would think would culminate in him finally meeting Maggie ... except now that Molly has been forced to become the Winter Lady on Harry's watch, he probably won't have the nerve to visit the Carpenters for fear of how Michael and Charity will react to that!
Speaking of the Carpenters, how will any of them react to the news that Molly has become a faerie Queen? Does this mean her soul will spend eternity in Faerie and can never go to Heaven?
At first, it seems like for all the bad things that would happen if Demonreach exploded, killing millions of people and wiping out a good portion of the United States, we could have taken some comfort that the explosion would have happened on Halloween Night. The time when all of those horrible immortal nasties are mortal, and can actually be killed. It is likely that the ritual to destroy Demonreach was originally created by Merlin, or someone working with him, and specifically designed to be cast only on Halloween night, specifically for this purpose. What makes this horror instead of brilliance is that the setup of the attack as described by Demonreach and elaborated by Odin. The attack spell was set up through space and time. Harry stopped the ritual on Halloween night, but if he hadn't, the spell would have hit and the island gone critical the following morning. Arguably, that's even better for Nemesis if it could trick the ritual into starting, setting up the prison breaking open, and then fudging things so that the explosion happened at a time when the prisoners could not be killed.