My opinion is Nemesis IS the corruption.  It sounds much like Hastur from Lovecraft

"Hastur (The Unspeakable One, Him Who Is Not to be Named, Assatur, Xastur, H'aaztre, or Kaiwan) is an entity of the Cthulhu Mythos. "

Hastur's main weapon is to instill insanity in it's victims minds.  The people often create a symbol that they show to other people, and supposedly anyone who sees the symbol is capable of being influenced by Hastur.

I always pegged Hastur for an Odin type, being a Wind deity, having power instilled in a rune, ect.

I do agree that it's not all powerful.  It may be similar to being connected to a Coin.  Most people seem to succumb, but if the will is there they can refuse it.

Exactly why it's so unnoticed amongst Humans, We've always been free to ignore the devil on our shoulder. And why it's comes to a head in Warlocks, they are making choices and becoming more of what they are in doing so. Harder to push against something that starts to be part of whom you are on an active creation level.... Think about it this way(cause I do lol) the Devil is free to whisper to us all he wants(or he used to be before being trapped) and as the Adversary, something given an active position in Bibliography, Nemesis's role is to do the same now?
*this ties heavily into the idea of the personal vs united shadow, the references to the devil within us, not our dark side, but the united aspect that that represents the interchangeable darkness. If Nemesis is humanities shadow until we trade into one specifically, Like Harry did with Lasciel. Lasciel broke the rules in CH because she was not supposed to act outside the coin, even though she already had Harry mirroring her from before. The proper person whose supposed to be whispering at us is Nemesis. The Denarian's procreate darkness and apocalyptic aura's thereby distilling it from building up while simultaneously eating up the soul of the host and creating a mirror, ergo stopping N and her cohorts from doing either, and remanifesting through the Denarians, or anyone else since the denarians are already holding the inside reality mirror for those aspects that they are relative to. The Denarians are part of our immune system.

I've never been able to decide how I felt on that one. On the one hand dark magic and Nemesis are certainly connected, on the other I see no real reasoning why Nemesis would step in to protect Harry here from being influenced by the seething mass of dark magic around sells house. How, cosmologically, that might be enabled or reasoned out or why She'd care. I'm more of an opinion it was his mother, but the two are not mutually exclusive necessarily.... I mean If Morgana's Atheme has a main line connection to N and Margaret is the spiritual successor to the Le Fay name, then I could see her being the influential person mirroring the original and ergo connected similar to Molly's connection to the WL position. But that still wouldn't explain a lot about the situation.

Sorry...  Just don't think that Mother Winter would allow an Outsider, or Old One to watch the Gates for Nemfected people.  That's like having a fox keep an eye on the chicken coup.  Also don't think of Rashid is someone who delights in pain, and suffering.

Your limited in your idea of MW, it's based on nothing in the book, she's not from our world either, an she's not exactly cosmically unbound to reshape reality to her will. She IS an Outsider. Your idea on Rashid is also similar to saying Santa would never hurt people cause that's not our perspective of Santa. It's in and of itself moot to the credence of the details themselves.
I mean his formation is not that hard to understand in the cyclic nature of things, take DR and have Harry darkhallow on it while containing the seething mass of monstrousities beneath his own strong will and beliefs. He would basically be Nyarlahotep, the  enlightened one, the rightly guided one... The earthly soul to the spirit of the Outer Gods. His cloak as dark as night itself, blah, blah blah.
Funny thing is if i'm right we get to see this one happen in the past-future and then I gloat maniacally at the limitation of others and know that all this time spent alone in my enlightenment was not for naught.

That could work, it doesnt contract anything we know as fact, but I also see almost no in-world support for it.

Matter of deduction, look for Lachesis and you find her in the power of wizards and wizardry, Look for Nemesis the Greek Goddess whom apparently hunts all fae, or all reality depending on context, and you find her scales being balanced by the courts and her aspect of Judgement taken by Mab when needed... So parts of her exist in the courts lending credence to her being taken by the stone table, which then lends it to the idea above that Dead but not forgotten matters(dude, you know Mexican mythos or the day of the dead/land of the remembered?) Let's see, Chronos is also known for being dead, and he's apparently the captain in charge of hwwbh being the slowest terror humans will ever know and all. I could make more connections but really, Nemesis should really be enough.
Why she's not part of reality even makes sense, she was the chooser of fate, to defy fate, to make a choice in the face of it is Hubris in the face of the Gods and worthy of destruction... and Marcone showed exactly that making a free will choice is Hubris to fate based beings, and then in direct contention with TWG's own designs for creation. Lachesis... she chose not only for herself but for the Gods themselves, something hinted at in Mortal Magic's ability to screw with the fae Alloy and let Nemesis find purchase. They took her power to choose and gave it to the Druids, Celtic magic users whom were subsequently wiped out by Rome but could whip up firestorms and other fantastic things... BUT could NOT effect fate..(Irish based mythos... evolved into fae too) Now Wizards can though. The took her power and rebalanced it in the human equation, and the only thing that makes it viable is not breaking the Laws designed to keep free will intact. Any breaking of these laws would, per PG, tend to make you a mirror for Nemesis herself then. And using it to cause fear while taking free will would sync you up pretty nicely to Fearbringer wouldn't it? hence the goal of N in PG, and Mab's counter move by having the fetch eat up Molly's N-fected soul parts.

Nyarlathotep would open the gate on a whim. For a laugh.

He did open up reality, that's how he became the gatekeeper.

Also, Gatekeeper if officially the guy who killed Abdul Alhazred (which, um, the proper name would be Abd'Al-Hazred).

Yea and the father of the previous GK was Dante Alighieri and that was wrote in... what 1300's and yet GK was around for thousands of years before that... So something is a Little Fishy over here too Black Cat guys...

Dunno, so far I haven't seen an oddball theory come anywhere close, and I'm pretty confident they're not going to.

Challenge Accepted. See any one of my theories on Arthurian legend, or pretty much anything to do with the gyre or history repeating or ect.

dread reading the next book for fear some of the theories you found distasteful and that have been argued on this forum might come true.

And every time a new book comes out I relish the look on peoples faces when some of mine do come true mwahahahaha.

Ah, ok, that makes way more sense than what you first said, which was that the Oblivion War would somewhat LEAD to the Outsiders return/awakening as opposed to preventing it.

As the theory goes: The Oblivion War works only on the premise that the targeted Creatures REQUIRE a connection to Mortal awareness in order to manifest in the Mortal World, or else they have no grip on the reality and are left floating in the distant unconnected reaches of the NN.  This makes fine sense for all the NN demons etc that keep being mentioned as having varying degrees of interest in the Mortal World.  It makes less sense in the case of the Outsiders because a)Outside and Oblivion are different things, and B) Outsiders dont /require/ a connection to Mortal Awareness since they are currently attempting to get in via other means.  The fact that there is a constant conflict at the Outer Gates being waged unknown to mortal race would strongly indicate that they do not have the same requirement for Mortal Awareness that NN natives do.  So the theory goes, anyway.

Ah... let me attempt to smash this one. Outsiders... look at Fearbringer, the idea behind him has not, and maybe cannot be forgotten by humans until humans no longer have a concept of fear, so, fear will always have a representation in reality. The same thing with Hwwbh, he's actually a psychological part of humanity,(i'd have to find the post on the jbit that has the right link to a really good article on it) the 'demon' you can't quite look at, that which stalks us all, Death.
To be expelled from reality in my opinion simply means you have no creation oomph, no payment on Rent or Purchase in the positive. Maybe even YOU died, even if your idea did not, in which case, as I suspect, Outsiders are the versions of Idea's/god avatars who died, maybe even the originals, and those who were intentionally left out of the little playground our God made.  BUT, whom are not forgotten, whom we actually put in our own mythology for their deaths, who we also remember are not exactly all good with reality or humanity,  Some of which only existed perhaps before reality truly began.
Look next at the Lord of Slowest Terror, Time, Chronos, whatever you wanna call him. His being dead/torn apart is kinda necessary for reality because of space-time. That's one of the clue's left for us, Outsiders get in, everything Stops. Because Time is no longer in pieces?
So this could also explain, in part, why the Outsiders look different trying to get back into any specific reality but are at the upper Echelon's all connected, they are from before the concept of reality, and we, Humanity, have had those concepts of before existence for quite awhile too, we just have names and identities attached to them. But if those identities are already dead but not forgotten? Outsiders and the need for Oblivion wars...

.... Ya'll keep annoying me by ignoring GK as Nyarla ima have to strong arm you into listening. Let's see, soul of the outer gods... position as Gatekeeper, compared to Warden, if you look it up, is the same job duty, even in the dictionary they are the same actually

Warden 12 A gatekeeper

Gatekeeper 2 guardian; monitor:

GK is obviously a previous version of the Odin/Merlin/Harry rotation right? Do we all agree on that much btw?
GK's appearance is actually a mantle from when he has human/mortal, It's the gooey center that let Uriel transubstantiate. Some proof is in the scaring on his face, a wizard would have healed over the centuries until it was faint but Harry describes it as deep. But also why he's connected to time and knowing the future, He's on a similarly Outside time existence, in fact, quite literally parts of him are beyond time, the Old God's part. It's why he see's time differently and see's future events.... and why he stays out of it mostly except like Uriel or even Odin, to enable a choice.
Back to the Soul of the Old Gods, he's known for having thousands of forms, that's why his mortal form is his usual Mantle when he makes an appearance, when reality is unbalanced he's the first thing to manifest that imbalance. He's their soul because like with the fae mantles his soul is attached to their spirit, he's the host. His timeline ended opposite Merlins, instead of creating a prison by sacrificing his soulfire into a construct(look at DR again... Death Blessing indeed) he contained them within himself.(a prison is made in each rendition of reality, slightly different, but similar. Hades, Hell, DR, Gatekeeper.....)The darkness within the Joy he also contains, just like DR, Controlling the Ugly with the Beauty. It's why he can't step on DR, he's not from here and DR remembers this.(there's a lot more to that but that's for believers anyway lol)
More stuff, someone go ahead and argue this one please, I'd love proving what I know on this one....

*OP, the 5 LC gods would easily align with the 5 main celestial Bodies in Greek astrology, the 5 epochs in Mesoamerican mythology, ect. So... mayhaps?