Richard the Unclean

Previously unknown evil man has a private dimension in his skull. His brain cannot be damaged unless the force enters his place, and reaches his mind's core. Information still passes from senses and to body from mind, but he is a form of undead. His physical body can be damaged, but regenerates even if from only his untouchable mind. Arrows piercing his skull travel in his dimension until they lose momentum. Melee weapons are lost, even lances entering his skull simply fall into his dimension. Heroes must use a form of dimensional travel magic to break into his mindscape to kill him.

"You're a dirty dick."