The Death Guard hold little love for sorcery, and the psykers in their ranks are regarded with wary contempt, yet the Malignant Plaguecasters endure and even flourish, thriving amid their brethren's scorn like sickness in an unwilling host. Each has bargained away what tattered remnant of a soul he still possessed for a share of Nurgle's power, and his flesh has paid the price, warped and flyblown from pallid skin to churning, distended gut.
A Plaguecaster's body is a living conduit to the Garden of Nurgle. Within his bloated frame roil flesh-eating spores, droning plague flies, corpse-gas and vomitous mist, the raw matter of the Grandfather's realm, held in check only by force of corrupted will. In battle he draws these miasmas up from within and breathes them out across the foe in phlegm-thick clouds.
Where that pestilent breath settles, warriors drop choking as their lungs liquefy and their flesh blackens and sloughs from the bone. Armour corrodes into flaking rust, weapons spark and die, and even sealed bunkers offer no refuge from the seeping rot. The Malignant Plaguecaster is proof that, for all the Legion's disdain, there remains a place in Mortarion's host for those who would wield the Warp itself as a weapon of plague.