[Libris Mortis featured a variety of elemental-themed undead, as well as a “necromental” template. In my conversions, I struck and reversed it, making them all undead-themed elementals.]
Cinderspawn
A lump of charcoal in the shape of a crook-backed humanoid stands and
glares with hateful eyes. Wisps of gray smoke pour from its body,
obscuring its facial features.
Cinderspawn are created when a fire elemental is inundated with water
infused with evil and negative energy, such as that of the River Styx.
Cinderspawn are infused with malice for all life, but especially despise
beauty—their own lovely flickering flames have been replaced with dull
char and ugly smoke. A cinderspawn’s actions are driven by this burning
resentment, leading them to vandalize works of art and try to murder
creatures lovelier than they. The searing flames of a cinderspawn leave
welts and scars on both the flesh and the soul, spreading their ugliness
to their victims.
Shores of Swords 