The festerhulk looms on a titan's frame, its hide a patchwork of swollen shelf mushrooms, bruised blue and violet, stacked like crumbling armor over dissolved ribs. A lipless maw gapes where a face should be, lolling a black-mold tongue amid purple mycelium curtains that drape its hollow chest. Ropey root-tendrils drag and twitch from the cavity, spilling spores like dirty snow that cling to skin and seep into wounds. Fresh pale caps gleam wet on its arms and thighs, feeding on the rot within as it lurches forward, recoiling from sunlight that crisps its edges.
Festerhulks are dead giants whose corpses are infested with fungus engorged by the magic of decay. This fungus has consumed and replaced much of the giant’s flesh and now animates the corpse. The heads of these giants are often completely overtaken by repulsive mushrooms and other fungal growths. The spores given off by their infestation can spread to victims killed by festerhulks, giving rise to further Undead.
Festerhulks shrink from sunlight, which harms the fungus that animates them.