Phyrexia

"All will be One"

-The Machine Orthodoxy

Phyrexia is not real. It is a myth, a cautionary tale, a legend so old most gods grew up thinking it an obscure warning to all who would call themselves divine. The tale varies, but always speak of a mortal with great power over magic. Sometimes he is human, sometimes a beast that rises to intelligence. But always a mortal being that discovers the secret of divinity. The Gods of the age did not appreciate anyone making their way into their ranks, let alone a mortal, so they imprisoned their new peer on a demiplane called Phyrexia.

History
If Phyrexia was more than a myth, accounts of it are rare in the extreme. The few material realm scholars that know of the myth know at most that a mortal being (most likely humanoid), in this age known as Yawgmoth, discovered how to become a god. To prevent his ascension or to contain his power, the gods sealed him on a demiplane of his own making, the realm he planned to make his divine seat of power. The seal was akin to the one used to lock away Rovagug, and as such was very near perfect.

For untold millennia, the myth of Phyrexia was only that, a myth. A cautionary tale for those who would seek to stand among the gods. The only real reminder left in the multiverse was a creature known as Sheoldred, rumored to originate from this mysterious place. That was, until Morrin Vellow suffered a powerful magical mishap while trying to bend the use of a planeshift spell. Vellow, perhaps after having interacted with Sheoldred on more than one occasion less than a year prior slipped through a crack in the seal and found himself on Phyrexia. Here, he befriended a local troll by the name Thrun and established a interplanar antenna that would allow him to shift to Phyrexia with less difficulty.

Vellow would later return to Phyrexia with his allies, Garrok Streitgeist and Jund. Both would react strangely to this realm. Streitgeist discovered powerful nanite-like particles in the air everywhere, and repurposed them to repair and revive his fallen disciple, Stannum. Jund was promptly abducted by Sheoldred and taken to Yawgmoth who still rules Phyrexia as its god.

The rest of Phyrexia's history is unknown to any but its inhabitants and the gods that helped seal it away. For now.

Phyrexian Oil
The most sacred substance to any member of the Machine Orthodoxy, Phyrexian Oil is a volatile and magically infused type of technology. Essentially nanites with a direct connection to the powers and mind of a god their primary function is to restructure all that exists to conform to the will and aesthetics of Yawgmoth. Phyrexian Oil is everywhere on the plane, in varying concentrations, but it never falls below a thin, imperceptible mist permeating the whole plane, even in its upper atmosphere.

The Five Suns
Phyrexia was fashioned whole-cloth and disconnected from the multiverse in all but the most tenuous ways even before it was sealed away. As such, the natural tides and eddies that keeps a given plane in internal balance and able to sustain life were disrupted if not completely blocked. In an effort to ensure the habitability of his world, Yawgmoth constructed satellites the size (but nowhere near the density) of Phyrexia itself to orbit above. These he infused with forces, both magical and mundane, harvested from across the multiverse and calibrated them to radiate the laws of nature through the spacetime of Phyrexia.