Melkoric Vampires (Or."Lûgât" S."Agarluistath") were not the blood-drinking undead spirits of Men; rather they were mighty Demons. These Spirits were once the patrons of harmless normal Bats, but under Morgoth's tutelage they became great doers of evil and sources of terror. They were mighty fliers, and in early times Morgoth frequently used them as messengers. Appearing as gigantic Bats with the faces of hideous Men or Women and the feet of enormous birds of prey, the Vampires were well-equipped to deliver the orders of Morgoth and to spy for him. Vampires could assume other forms by means of their magical shaping cloaks. (These cloaks could also give others the power to take on the shape of Vampires).
True Vampires, like Thuringwethil or Gulavhar were powerful Maia-Spirits, lesser Vampires, as the Morroval and Morvul were just the weaker Maiarindi-offspring of corporeal Maiar and far smaller and not truly immortal.
In MERP the Term Vampire is also sometimes applied to mannish-Vampires, Undead men, defacto false-ghouls created by sorcerous experiments who tried to expand their life by the consumption of blood.It also knows a type of undead Shapeshifters who magically drain their prey, known as Blood Wights.The Merp Adventure "A cause of Death" by Jon Sutherland & Simon Farrell features a vampiric disease spread upon humans by magically infected birds who had devoured the remains of a defeated "true Vampire".