Found it! The actual spot in Planewalker is missing, but the big thing itself is still floating around at different parts of the internet.
"Listen up, berk, because I'm not talking just to hear my bone-box rattle.
There are three rules to everything. The Rule of Threes, the Unity of Rings, and the Center of All.
The Rule of Threes is easy to see. There are three levels of existence: the Elemental Chaos, the World, and the Astral Sea. The World has three layers, too: World, Feywild, and Shadowfell. The Elemental Chaos has three layers: Deep chaos, the stable realms, and the Abyss. The Astral Sea has three layers too: the sea itself, the Dominions, and the trackless sky above it.
The Unity of Rings is harder to discern; you have to be a true blood to see the dark of it. It means everything that goes around comes around. Life comes from death, and death comes from life. Fire becomes ashes, which become earth, which become wood, which burn again to fire. Evil turns on itself. Day becomes night becomes day, summer becomes winter which becomes summer. They say if you travel the Astral Dominions long enough, you'll end up back where you started. They say the World is circular, like a ball. They say the Abyss devours itself like a snake eating its own tail.
The Center of All means you're not as important as you think you are. The planes don't revolve around you or your little kingdom or your little world. No matter how big you think you are, there's always something bigger. It also means you are the center of the multiverse because every point is equally the center of it all. No matter how insignificant you think something is, it just may be the crux that holds everything together, because everything is the crux that holds everything together. A butterfly's wings in Bytopia might create a storm in the Shadowfell that sweeps across the boundaries between worlds, destroying a realm in the Elemental Chaos and stirring up thoughtwinds that drive them mad in Pandemonium. This is the secret the Sign of One know, how to take advantage of the fact that they are the creators of the multiverse, because all of us are, all of the time. We dream the worlds into being.
Where is Sigil? It's in the space between night and day, between dream and memory, between thought and action, between chaos and law. It's between this moment and the next. It's between yesterday and never. It floats in the womb of unborn worlds. It's on top of infinity, and at the bottom of nothing. Some say they can see it hovering in the sky in the Astral Dominions above a mountain so high that you could climb or fall from it until the end of time or the beginning and never reach your destination; I never have, but maybe I just haven't found the right Dominion. Who knows? If Sigil is really the Center of All, it's everywhere and nowhere. You'll find its doors or you won't.
Who is the Lady of Pain? Some say she's a Primordial who betrayed her own kind to the gods, and others say she was a god who betrayed her kind to the Primordials. Some say she's nothing but an illusion, or a rumor spread to keep the citizens of Sigil in line. Others say she's an elder fey, or a human sorceress who got lucky, or a shadar-kai who stole some of the power of the Raven Queen and found a place to hide from her wrath. No one's learned the true dark of the Lady, not ever, and I don't think anyone ever will. You'd have an easier time finding the center of a ring."
