Miasmic Malignifiers are Death Guard foetid furnaces, which contain vile fluids that are spewed forth as toxic fumes from their chimneys.
This Putrescent Fog makes the Death Guard even harder to kill and a Malignifier is so contagious and foul smelling that their nearby enemies suffer terribly in its proximity. Even if one is destroyed, the furnace will likely burst in a Putrid Explosion.