Sleepwalkers

"Sleepwalker. n(noun). Nomadic shape-shifting creatures with human and feline organs. Vurnerable to the deadly stratch of the cat. The sleepwalker feeds upon the life force of virginal human females. Probable source of the Vampire legend."

- Chillicoath Encyclopaedia of Arcane Knowledge 1st Edition .1884 (about the Sleepwalkers).

The Sleepwalkers are an ancient and forgotten nomadic race of vampiric shape-shifting werecats. They possess magical powers, and among their gifts is the ability they called "dimming" which is make themselves and any other object within their presence invisible. The only two known members of this species are the widowed mother Mary and her son Charles Brady, the two main antagonists of the 1992 horror film Sleepwalkers (Stephen King's Sleepwalkers).

Origins
Thousands of years ago in ancient Egypt, the Sleepwalkers who are Earth-born human-like beings, were once worshipped by humans as gods. They possess such supernatural abilities including the "dimming", or the ability to turn themselves as well as any other object or person in their own presence invisible. They must feast on the life energy of virgin girls in order maintain their youth and strength. They are also immune to any injury except those inflicted by a cat which are to them extremely deadly. Once this mortal weakness was discovered, they were renounced and even shunned as monsters and demons.

Centuries passed and the Sleepwalkers were branded not just as monsters, but also as witches and warlocks. They appeared many stories and legends. They continue to hide in obscurity. It is once said that they have been having incestuous relationships in order to continue the species.

The 2 Sleepwalkers
Charles Brady and his mother Mary are Sleepwalkers. Though they normally maintain a human form, they can transform (partially or fully) into human-sized bipedal werecats (presumably their natural form) at will.

Charles and Mary have taken up residence in a small Indiana town of Travis, having recently fled Bodega Bay, California (where they used the aliases Martha and Carl Brodie) after draining and killing a young girl there. Charles attends the local high school, and there he meets Tanya Robertson in his creative writing class.

Tanya does not suspect the real reason why Charles is interested in her; to take her life force for both himself and his mother, who is starving. At first, it seems that Charles has genuinely fallen in love with Tanya (to the dismay of his jealous mother). On their first date, however, a picnic at the nearby cemetery, Charles attempts to drain the life force from Tanya while kissing her. Tanya tries frantically to ward off Charles by bashing his head with her camera, scratching his face, and ultimately plunging a corkscrew into his left eye.

As it happens, Deputy Sheriff Andy Simpson (who had earlier tried to pull Charles over for speeding and passing a stopped school bus, and seemingly trying to run down a young school girl) drives by the cemetery and notices Charles’ (now undisguised) car. When Tanya flees to him for help, Charles attacks Simpson and kills him. When Charles then turns to resume feeding off of Tanya, the deputy’s cat, Clovis, rises to the occasion and nearly kills Charles by scratching him in the face and chest. Mortally wounded by Clovis, Charles staggers back home to his mother who is able to make both of them "dim", i.e., turn invisible, and thus keep Charles from being arrested when the police storm their house.

Knowing that the only way for her dying son to survive is to feed, Mary attacks the Robertson household, killing the entire sheriff's department and severely wounding Tanya’s parents in the process. She kidnaps Tanya and takes her back to her house, where Charles by this time is all but dead. Mary revives him, and Charles makes a final attempt to drain Tanya’s life force. However, Tanya plunges her fingers into his eyes, killing him. Tanya manages to escape with the help of the sheriff who is later impaled on the picket fence surrounding the house by Mary. Several of the cats that had been gathering around their house throughout the movie, led by Clovis, jump on Mary and claw at her until she bursts into flames, killing her. It ends with Mary lying ablaze on her driveway and Tanya hugging Clovis, her savior.

Somehow true to Mary Brady's last words that she and her son Charles were not the last of their kind and there are many unseen but remaining and surviving Sleepwalkers out there in the world.