This “living vampire” is called tlahuelpuchi or tlahuihpochtli in the Nahuatl language, a term meaning either “glowing haze” or “illuminated youth.” They are so-called because they emit a telltale light when they hunt in their shapeshifted form. In Spanish, this is rendered as “luz que se mueve,” “luminosidad andante,” or similar. The plural form is tlahuelpocmimi. In Spanish, they are sometimes simply called brujas or “witches.” Another term describing a similar creature is tlaciques (both singular and plural).
Tlahuelpocmimi hail from central Mexico, specifically the small state of Tlaxcala. They are associated with the Aztec god Tezcatlipoca, the “smoking mirror,” god of the nocturnal sky, ancestral memory, time, and change through conflict.
They can be of either sex, though females are more powerful than males. They are adept shapeshifters, usually attacking in the form of a vulture or wild turkey. They also sometimes enter a victim’s house in the form of a mist. It is said that when they shapeshift, they leave the lower part of their bodies behind.
Tlahuelpocmimi are victims of a curse. They grow up normally until their monstrous nature becomes evident at the onset of puberty. They live with their human family, which guards their secret out of shame and fear, and many believe that if a family member destroys them, then they will become the next to inherit the family curse.
These vampire-like creatures have their own society parallel to that of humans. They form pacts with one another so as not to infringe on each other’s hunting grounds. They also forge pacts with shamans not to turn on them. In fact, they sometimes do a shaman’s bidding in exchange for this protection.
These creatures possess many of the weaknesses associated with classic vampires, and it’s not clear whether or not this is the result of cultural cross-pollination from Europeans. They are, for example, averse to the holy and to objects of silver (some say any metal). They are repelled by garlic, onions, and mirrors. Like other vampires, these creatures cannot normally cross a threshold unbidden. If, however, they first fly over the house in the shape of a cross, this impediment is removed.
Tlahuelpocmimi are driven to feed on children, and some say they must feed at a regular interval (once per month, once per week, etc., depending on the source) or die. When they feed, they always kill their victims.