The College of Mensis are all lactose intolerant
Hear me out. As everyone knows, cheese gives you nightmares if you eat it before bed, and the moon itself is also made of cheese. The College of Mensis "toiled surreptitiously in rituals to beckon the moon" and transplanted their entire organization into the Nightmare, so it would make sense that in an effort to induce nightmares and therefore commune with the Great Ones of the dream, they would eat copious amounts of cheese. However, I believe this backfired horribly due to them all being lactose intolerant. The severity of their diarrhea killed most of them, which is why their mummified corpses are all sitting in the room beyond the One Reborn's arena; you see, "Mensis" is Latin for "month" and comes from the same root as "moon", and the Romans, who spoke Latin, used communal public bathrooms where everyone sat together on toilets, which indicates that the Mensis corpse room is a similar communal bathroom. However, some of them survived in the Nightmare, like Micolash: his bossfight provides several hints towards the fecal fate of the College. For one thing, his bossfight is absolute shit, just like diarrhea, and because of this people like to kill him with poison knives - a cheese strat, like the cheese he ate that gave him the diarrhea in the first place. For another thing, he has a stupid fuckass oneshot AOE attack that resembles clouds of gas erupting from a hole, just like a fart, which is not only another consequence of lactose intolerant indigestion, but referred to as "cutting the cheese". So if the College of Mensis shat themselves to death from lactose intolerance, where did all the shit go? It's the One Reborn. The principle of communing with the Nightmare via cheese was sound even if the bodies of the Mensis scholars were too weak to make it work, and the great mass of their dairy diarrhea was linked to the Nightmare, though it could not become a true Great One. We know this for a few reasons. First of all, the One Reborn literally looks like a big pile of shit, and it even has an attack where it leaks acidic fluid everywhere, just like when you have diarrhea. For another thing, its bossfight is also shit. Finally, it falls from a big dark hole that obscures the moon; dark holes are obviously anal in symbolism, which is why Michael had to change the name of Dark Ring to Dark Souls because Dark Ring is like Dark Hole which is an anus, and the moon, in addition to being made of cheese and thus hinting at the origin of the One Reborn, is also associated with asscheeks via the phrase "mooning". The One Reborn literally falls out of an asshole on a butt, just like shit. But where did the cheese come from in the first place? Well, most cheese is made with milk, and as it turns out, the Mensis scholars may have had access to milk that would allow them to commune with the Nightmare. At the very peak of the Nightmare of Mensis lies Mergo's Wet Nurse, a Great One in truth, and what does a wet nurse do? They feed babies with their milk. It's all connected, or some say interconnected. Bravo Michael Zaki