A valfither, also known as a witherer, is an undead creature identifiable by its odd, glowing head of pure light upon a rotting body that seeks the heads of living humanoids. It tends to wander locales around where it originally died at the hands of another valfither, generally in forests and ruins, speaking to potential victims in a calm and reassuring voice to lure them into its grasp.
Valfithers usually only target solitary creatures, lowering their defenses in order to touch them, an act that saps the strength of the victim and eventually turns their body to rot. The creature will then attempt to remove its victim's head to place upon its own body, which will allow the vilfither to live as a normal creature for one year before becoming undead again, when the stolen head turns to dust. The beheaded victim will become a valfither over a period of around 5 days, with a tortured head of full light, perhaps a twisted incarnation of the victim's soul, longing for a head to make it complete again.
If a stolen head is returned to the valfither it was taken from before a year passes, the valfither's broken soul will become whole again, and it will be able to resume a normal life.