Shtriga

Shtriga is a creature that feeds off of Children' lifeforce, and takes on a friendly appearance in society. The word Striga in albanian means "witch".

Background
Pre-Season 1 Sam and Dean first encounted this when they were kids. John left Dean in charge of taking care of Sam, while he went to hunt this creature. Dean went out later that night and found the Striga feeding on Sam. John comes in at the last moment and shoots the Striga.

Season 1
John sends the boys to a town where this creature is so Dean can finish the job. The Striga takes on the form of a doctor who is taking care of the ailing children. Sam and Dean kno'''w its pattern and set up a trap for the Striga by using a boy. When the Striga gets close enough, they pop out and attack. The Striga manages to overwhelm Sam and begins to suck his lifeforce, until he is ended by Dean.'''

Abilities
Live forever: by feeding off life force, the Strige can live for a long time.

Drain Spiritus Vitae: Striga's can remain immortal by sucking the life force out of childer. The life force that Strigas suck out is call Spiritus Vitae with is latin for "Breath of life"

Near invulnerability: Striga's are very difficult to kill. They can't be kill with normal weapons like guns and knives, but Strigas can only be killed when it is feeding and then shot with iron bullets.

Human disguise: By day a Striga can take a human disguise, so that hunters won't be able to detect the witch. At night the Striga transform back to it's hag form.

Superhuman strength: Although most witches have normal human strength, Shriga possess this ability. They can easily overpower humans and lifted them and throw them with great force.

Superhuman speed: Strigas have move faster then humans. They use this ability run to from danger or for defense.

Weakness
Can only be hurt while feeding, and shot with an iron round.