Venser is unsurprised that Koth knew nothing of Karn, but before he can enlighten them, they find the Mephidross, stretching farther than he or Koth could possibly have expected. Looking for Koth's acquaintance, the group is ambushed by nim. The allies quickly fight off the nim, but before they can plot an expedition deeper into the swamps, Elspeth tells the arguing walkers that she cannot go any further.
Unfortunately, without her warrior's expertise, Venser and Koth fall quickly to a Corrupted Harvester and are dragged back to its lair near Ish Sah. Koth awakens under harsh lights strapped to a table next to his reluctant ally. He quickly frees himself, but cannot rouse Venser before the Phyrexians come. He wards them off, but is overpowered as Venser prepares to teleport them both out of the surgical theater. His plans are disrupted by Elspeth's sudden reappearance. With her help the trio subdue their captors and proceed to the Black Lacuna. Venser teleports inside for recon and is horrified by the sheer number of the forces within.
The Sylvok outcast Melira tells Venser and his party that the oil only turns a being into a full Phyrexian if the heart is fully corrupted. By the time Venser reached Karn in the core of Mirrodin it was already too late. Melira cleansed the golem's body of the Phyrexian taint but she couldn't cleanse the golem's heart. Knowing his own life would soon be forfeit due to his increasing affliction symptoms, Venser made the ultimate sacrifice. With his last remaining mana he teleported his own still pure heart into Karn. Moments later Karn was released from the Phyrexian tyranny and mourns the loss of his friend briefly but turns to battle the Phyrexians, stating 'he still has a lot of work ahead of him'.