The Next page contained a description of Karn.
"Karn, Planeswalker.
As he surrendered his Planeswalker spark for the sake of the plane of Dominaria, Karn flung himself to the metal world he had once created. Stranded on Mirrodin amid a newly developed Phyrexian system, Karn's mind became unhinged, and the influence of Phyrexia festered and grew inside him. Deep within Mirrodin's core, the trace of glistening oil the silver golem had left on his plane centuries ago had become the seed for a reborn Phyrexian civilization, leaving Karn himself trapped within its widening web.
In Karn's throne room and prison, Phyrexians groomed and nurtured the mind-injured golem, plugging him into a specially constructed Phyrexian throne, harvesting his ravings as scripture. At times, Karn was a full-blown Phyrexian leader, uttering commands to destroy Mirran life. Karn was occasionally lucid enough to struggle against his Phyrexian corruption, but the Phyrexians acted as jailers, preventing his escape and traumatizing him back into submission.
The five Phyrexian praetors waited for a sign from their adopted "Father of Machines" to seize the Mirran surface. when none came, their individual dreams of power urged them to look beyond--and at last they got their wish. The sign came in the form of strange beings -- planeswalkers-- intruding into the Vault of Whispers, the main Phyrexian access point to the surface. The praetors took this event as their cue. Countless Phyrexian killing machines of every shape and size poured from Mirrodin's five lacunae. the war had begun, and although the Mirrans made a surprising strong stand, the outcome was never really in question.
Even as Mirrodin fell to Phyrexia, Karn was liberatied from his prison through the efforts of Venser, Elspeth, Koth and their Mirran allies, regain his sanity and his planeswalker spark. Karn realizes his new purpose now. He can't stop Phyrexia, but he can use his former connection to Phyrexia and his status as the would-be Father of Machines to render inert the agent of coloniztion: the oil. he must retrace his steps and find the contagion whereever it lies, and nuetralize it. His taks and his mind are now clear: 'My world is corrupted beyond cleansin. I must prevent this from happening to others.' "
Whew, i got writer's cramp from writing that. Looks like Troy was right after all, Karn did serve the Phyrexians, he just wasn't poisoned per-say, and he never really told the Phyrexians to attack Mirrodin.
