Welcome to Mirrodin! World of Metal, created by Karn, planeswalker of Dominaria. Mirrodin has been infected by the Phyrexian oil, spread by Karn himself, likely from the corruption still present in the phyrexian heartstone within him, given by Urza Planeswalker, once owned by Xantcha.
Three planeswalkers gather- Here are the three sets of webcomics!
Scars of Mirrodin:
Convincing Elspeth and Venser to aid him, Koth, a native of Mirrodin, returns to his home plane to join the battle against newly forming Phyrexian forces. Elspeth had faced Phyrexians as a child on her homeworld, which was invaded as well. Venser, a native of Dominaria, had lived in their ruins and aided in the Mending with Teferi. He was still working on interplanar portal and teleportation devices.
Trailer (We will endure), Trailer (All will be one)
Phyrexia and the Vaultlord
Mirrodin's Human cultures.
A tale of two clone shells.
Non-human cultures of Mirrodin.
Why the Mirrans will endure.
Mirrodin falls, and the phyrexians have won.
Underling Ethu's 263rd report read simply "Yes, my lord. Overwhelmingly, my lord." This marked the end of the Mirran-Phyrexian War. -War Report, Card 26/174, New Phyrexia.
Planeswalker's guides: Part 1, Part 2: The Swarm, Part 3: Machine Orthodoxy, Part 4: The Quiet Furnace, Part 5: The Progress Engine, Part 6: The Steel Thanes.
Elspeth escapes with her life, and describes what happened after the Quest for Karn novel in a letter to Ajani.
There is an Ezuri, card, with him Phyrexianized in Commander 2015. He has been compleated.
Other stories from New Phyrexia:
Individual Character descriptions.
Farris of the Anvil
Unctus of the Synod
Roxith, Thane of Rot
Kessla, of Temple Might
Ria of Bladehold
Basic information on the plane: Wiki
The terms of Mirrodin.
Not much lore is told of the world otherwise, though the novel, Quest for Karn exists. It cannot be recommended by this blog.