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Omar.. I SWEAR get that damn thing away from me!

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Shows up at your house.
Omar.. I SWEAR get that damn thing away from me!

Anya is live and ready to show you everything. Watch her strip, dance, and perform exclusive shows just for you. Interact in real-time and make your fantasies come true.
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"bring it on!"
"that's a nat 20."
"...wait"
That's actually just—Mr. Poe. Or Ed Poe. Actually, it's Edgar. Or Edgar Allan Poe—just call me, just call me Mr. Edgar Allan Poe.
Edgar Allan Poe in Edgar Allan Poe’s Murder Mystery Dinner Party [x]
Lrb Micolash wearing this vest but instead of grey and white mice plushies it is brighter and paler hues of blue augur plushies
Edgar's 'spyoning' situation (theory)
Oh boy oh boy, here I go making theories again. It has been a while... *grinds dry lumenwood into dust and inhales it for more Insight* So, I was able to piece together some evidence but consider it an alternative take to commonly accepted one rather than definitive thing!
Okay, so:
As @saint-micolash already pointed out in discussion in this ( x ) post, despite what is easy thing to assume, other people in the ritual room are not 'other scholars', they are the captives! Notice that their cages are only four bars tall and they are missing uniforms, however have cuffs and even metal collars with chains on their neck!
We by the result cannot say whether other Mensis Scholars existed or how many, maybe Micolash and Damian were the only ones. ...or maybe, since they are refered as 'madmen', there were some other ones but they are long now killed by Micolash and Damian simply got away before he "expired his use".
Okay OKAY sorry I am sidetracking!
But my point is, it was probably very hard if possible at all to simply 'blend in' amongst other scholars with his outfit as disguise of sorts. Not only there is no evidence of there having been more scholars than just Micolash and Damian, but also sending Edgar over in a disguise would have to be done under assumption that he could blend in to the point of not being noticed.
My cornerstone therefore would be assuming that his spyoning was an act - he would allow himself to get "captured" and quickly make himself useful and pretend to naturally agree and cooperate with School of Mensis, knowing what to say to make it seem legit!
There is no dead body anywhere in Yahar'gul to display Edgar being in the ritual too, so if he was to get into Nightmare of Mensis from that point - he'd have to survive the ritual and then get there through touching Micolash's corpse, like how our hunter does. However, things might be even more interesting.
(Screenshots help from @majitek and @saint-micolash because I cannot play game and take screenshots rn)
Okay you got the idea, this is the corpse where Lecture Theatre key is picked from, dressed in Black Church hunter outfit! So, not a teacher. Ack, maybe hat lacks because it is overused model and they trid to avoid clipping, but whatever. I'd assume Yurie (and possibly Fauxsefka too) had some escort with them, which makes sense, it is too dangerous to go through Forbidden Woods alone.
(Screenshots help by @cuddlefish-fish )
These are some more, notably, one in Black Church garb too but the second one is in normie Yharnam Hunter garb. I think these people must have gotten here through secret passageway in Iosefka's Clinic! Think about it - what is the purpose of that secret way if there is Gatekeeper that has password every Church person must know ('Fear the Old Blood')? Well, perhaps "forbidding" Byrgenwerth was just a convenient lie so nobody would pry on the secrets of the Healing Church and where Old Blood really originated from! So they'd had to uphold illusion of not going there, but actually were using secret way.
The thing is? Edgar might have been amonst these people.
Lecture Hall is connected with Nightmare of Mensis and currently it is not possible to access Lecture Hall from Byrgenwerth area, but we do not know for how long that was the case!
(Excerpts from here ( x ) by Last Protagonist)
The last note nitpicked is interesting as in Japanese original it does not seem to outright imply Willem, it might refer to Oedon after all as he is indeed invisible/unencounterable, he is a voice! Rom is indeed consealing the ritual but as well everything else - like Amygdalae - so maybe that includes drowning Oedon's voice out too, especially considering where this note is found. It is a bit important back to back with the fact that Willem himself 'hid a secret in the lake', so more likely that Oedon Chapel note does not mean Rom is holding him hostage or something.
Screenshot help by @cuddlefish-fish again, who also pointed out to my attention how many of these Black Church hunters are over Nightmare of Mensis. These might very well be those that Patches lured into being snatched by Amygdala, but after our hunter survives abduction - Patches reveals they were meant as sacrifice to them, so saying they'd bring Church Hunters to Micolash is a bit of a stretch. Maybe they all just escaped and ended in Nightmare of Mensis through Nightmare Frontier, however some of them are pierced by Frenzy spears.
Okay one last bit, one last bit, trust me I am going somewhere:
Now let me try to lay my idea down with everything compiled! Okay so, we have - Byrgenwerth students 'still waiting' for Willem, Willem loving the look at the spot and having put Rom in there, Choir member(s) invading not alone but with at least some Black Church hunters, fact about Rom consealing 'all rituals' and not even THE ritual being known 'outside', Edgar being a spy of the Choir but unable to "blend in" back at Yahar'gul the way we like to think in memes, several Black Church hunters being in the Nightmare of Mensis with some Frenzied, Edgar dropping sedatives that are cure created at Byrgenwerth, Shadows of Yharnam that are also enemies in Nightmare of Mensis guarding gate to Byrgenwerth and Micolash mentioning that the lake is "no longer visible"...
Okay now imagine:
Rather than getting into Nightmare of Mensis through Yahar'gul, Edgar accessed it through Byrgenwerth! The passageway between 'reality' and Nightmare was not always blocked - back then one could jump into the Lake and BAM, Lecture Hall! Hidden from the n00bs. So Yurie and Fauxsefka were trying to send some low ranking Black Church hunters to scout the place, but they would all end up wandering into Micolash through Lecture Hall and those who survived to tell about it revealed some insane things before their eventual death.
So, while other scholars still have not quite became all slugs yet were instructed to 'stay away from the door', they were able to send Edgar under the guise of wayward scholar! He was prepared, being a good actor and packed with sedatives, and he could suppose what to say to play it cool and survive the encounter. Since Yurie is 'the last scholar' she probably was one of them too once, so I imagine she could fill Edgar in about Micolash, having known him before. Could have been Damian, too - he is a summon in Byrgenwerth and does not seem to be on the side of Micolash anymore... But these are just realms of further possibility. In either case Edgar was a very smart (and very brave) man and ventured in!
* It also might shortcut the explanation as to why there is Iosefka's blood vial in the Nightmare of Mensis - if they were friends passing through her clinic (at least until Fauxsefka lost her screws), maybe she simply gifted it to Edgar into adventure. It depends on what one wants to do with her, though.
But eventually Edgar broke under Micolash's influence. He must have a huge charisma as a Cult leader! Edgar did his best but only could have lasted for so long before breaking and, perhaps, ratting his true endeavors out. He acts very genuine in trying to kick our Hunter's ass, for Micolash. I like to think Micolash knew from the very start Edgar was not just an ordinary scholar and was secretly manipulating him.
Now with all found out, Micolash did something so the lake could no longer lead anyone to him - sending some Shadows of Yharnam over to block the way in and out, as one last gesture. The lake was "no longer visible", no longer the portal! Was probably some arcane water manipulation, maybe even aid from Kos herself. If she hates humanity, would not protecting ritual further aid that? So, water manipulation upon lake it is...? Maybe! And scholars did not have chance to evacuate, nobody could foresee that Lecture Hall and the main way to Byrgenwerth get split for good.
Perhaps Yurie and Fauxsefka got stuck for a long time in the place, until closer to the game events night, but notice the lack of Celestial Emissaries in Byrgenwerth - ones that Fauxsefka creates! She seems to be turning people into Kin so they don't have to become beasts instead which Yurie might not have agreed to. Choir operates differently but maybe Yurie was still more aligned with Willem's ways - something Fauxsefka eventually gave up on and ditched.
Interestingly, there is Cainhurst invitation found on the side of Iosefka's Clinic she invaded from, she also can create "secret" Cainhurst potions, and only her and Annalise mention 'moon scent' to our Hunter. Maybe she had means to 'pass' through Shadows of Yharnam as a vileblood and therefore 'their' person, leaving Yurie unable to chase her as Shadows would be too much for her. Or maybe she did not want to as protecting Rom was more important anyways?
---------------
I also want to give special thanks to @val-of-the-north because HE pointed my head towards random corpses in Byrgenwerth being maybe not so random and needing a closer look, and this is how I started to loredig this interesting bit! And to @saint-micolash because that single discussion and his remarks became a cornerstone of how I see School of Mensis now. Though overall I am very happy that this fandom is so helpful to my PS4-less ass, thank you so much guys for sharing screens and stuff!
Again, everything is only in the realm of possibility and could have stopped back in Yahar'gul, but I just thing everything is more tied together this way. And explains Mico's weird line about the lake...?

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Good god, I'm having a bomb dropped on poor Edgar and Idk how he's gonna recover from this.
Curtis is gonna fucking lose it.
Lancelot: *says anything
Jonah: *wiping away a tear* I abso-fucking-lutely agree
Edgar: h-
Jonah: I think the fuck not, you trick ass bitch
Felix, hugging VR Sven : i can actually feel you Sven
Felix : i can smell you too. You smell like a real dog.
Felix, takes off the VR : Edgar? You're not Sven! Get out of here!