I don't think that we will ever find out if Nemesis is of TWG's creation or not, because I don't think we will ever truly see TWG or get a real scope for His power.

We kinda have to, though. We're already on a collision course for an answer to this question, just with the Denarians. Why was Nicodemus so surprised by the attack on Arctis Tor? Was he surprised because it meant his other Denarians were "infected" (i.e., Denarians can be evil without being infected, i.e., not all fallen angels are infected, i.e., Lucifer != Nemesis), or just because it meant Lucifer was running a plot he didn't know about? Lucifer would certainly have the metaphysical oomph to mount an attack on Arctis Tor!

There are things we know the Fae don't clearly understand. For example, I doubt Mab has all that great an understanding of Summer, possibly including things like "summer emotions" of joy, hope, etc.

I expect that's part of why Mab can't quite predict Harry -- she can't quite "get" a lot of human emotions, just like Bob has a hard time understanding the concepts of Good and Evil.

The way I read "what stalks us all," I think Lea is speaking broadly.

If "all' means the  fae collectively? Perhaps the fomor collectively, perhaps Death, perhaps Cold Iron (perhaps as personified by Ferrovax?) Mortal technology? 

The impression I get here is that Lea is talking about something more powerful than the Fae as a group, or more powerful than the fae+humanity as a group. Something more powerful than Winter and Summer as concepts. Entropy, death, some primal principle.

Or maybe she just means the Circle / Black Council.

How do you get a Fetch to come to Earth?  Well, you need to summon it with a load of fear.  Enter Madrigal, puppet of the Black Council.  As Madrigal says, he was invited to come to the convention a year previous.  ...Right around the time the Darkhallow failed?

I'm not sure the Black Council was "desperate", or that the Darkhallow was their primary goal. I do think their apparent goal at this point is destabilization and chaos -- knocking over and weakening as many of the big supernatural players as possible.

Here's a question though: was Molly a target of opportunity, or the original plan? A horror convention with a Malvora in attendance is a great way to send in fetches to Chicago and give Harry something to do, but who knew -- a year in advance -- that Molly would be developing magical talent?  There is that quote in Grave Peril where Lea asks for Michael's eldest child, but that could be general "fae ask for eldest child" trope, not specific evidence.

Yet:
That doesn't sound like he's bulling through magic.

Edit: could anyone get the quote in Hereot when harry's magic is blocked? I don't have the text.

The grendelkin hadn’t been kidding about knowing counter-magic, though. All that naked force hit him and just sort of slid off him, like water pouring around a stone. It only drove him back about two steps—which was room enough to let me drop to one knee and swing my staff again.
 

The problem with the "ocean of cold, cold power" quote is that it's equally interpretable as "outsider immunity" and "ancient winter fae immunity." We already know the Scarecrow is an ancient, powerful, Winter fae, so that seems the simpler explanation.

Time isn't THAT screwy in the NN, even if it happened a year before PG, it would have been cleaned up by then. And the smell of Hellfire would probably be gone in half a day, tops.

Harry actually says specifically otherwise:

“It must have been weeks,” Thomas said. “It takes that long for bones to get this clean.” “It’s all relative,” I said. “Time can pass at different rates in Faerie. These bones could have fallen a thousand years ago, by the local clock. Or twenty minutes ago.”

Edit: Alternate Theory:

“Whoever called up these phages,” I said, “needed a way to guide them from the Nevernever to the physical world. They needed a beacon, someone who would resonate with a sympathetic vibe. Someone who, like the phages, wanted to make people feel fear.”

Butcher, Jim (2007-02-06). Proven Guilty (The Dresden Files, Book (p. 270). Penguin Group. Kindle Edition.

Lea sent the phages after Molly. We know from as early as Grave Peril that Lea wants Molly; she asks Michael Carpenter for his eldest child. She's high up in Winter and might reasonably be able to command fetches, as Mab's handmaiden and highest servitor.

The "Attack" on Arctis Tor was actually Lea with the Athame (and the Black Council?) attempting to rebel against Mab. Sure, that happened at least more than a year before (prior to Dead Beat, since Lea's imprisoned then) , but what's time in the NeverNever? Mab conquered the attack all on her ownsome, so no probs.

Of course this theory has the problem that Lea was imprisoned at the time, but perhaps she'd given standing orders to the fetches?

Hrm. Perhaps Lea had a standing bargain or deal of some kind that forced Mab to send the fetches.

Yes. But she's just making sure Harry pays his debt. Not kidnapping someone to force him to take more. I feel that if Mab was in the business of kidnapping people to get new debt, the WC woud try to stop her. Now you may say that she's too strong. In fact I'm sure that an alliance between the WC and Summer would be devastating for Winter.

Yeah, but the WC isn't going to rush to defend a budding warlock ! That just makes it fit even more! Molly's no longer an innocent, so nobody's going to defend her .. . except Harry. Or, well, her dad, and his cold iron magic supersword, so maybe this wasn't a perfect plan on her part after all . . . or maybe she planned on trading for the Sword. . .

Hrm, here's an idea:

What if Mab sent the Fetches to home in on Molly's magic -- precisely in order to make Harry *focus* on Molly's black magic, so that he could intervene early, before it sent her (and, with her, him, because he'd probably die defending her) off the deep end into severe warlockry and the sharp side of Morgan's chopper.

Mab's goal would just be "make Harry take Winter Knight" all along, but the Black Council is screwing that up by trying to seduce Molly to the dark side (for all the above reasons), which would make Harry implode because he's Harry. So Mab (with foreknowledge) moves to really ATTRACT Harry's attention to Molly's dark practice by sending Fetches at the victims and then snatching Molly so that she can try to trade her for the Winter Knight job.


Think about what would have happened if the fetches hadn't attacked. Harry would have left the convention and might not have ever investigated those goings-on enough to realize Molly was turning dark, not until she'd gone much much farther down the left hand path. The fetches don't make sense as a distraction, but they do make sense as a "hey, look at me!"