Ghouls

Ghouls are an evil race of supernatural creatures that have been encountered by Hunters and by Sam and Dean Winchester. The first time Sam and Dean have encountered ghouls was when they took on the form of their long-lost half-brother Adam Milligan and Adam's mother.

Ghouls are scavenger creatures that live in graveyards and traditionally feed on the flesh and blood of the dead. At times ghouls will change their diet and will feed on living humans instead of the dead. Ghouls will also take the form of people they eat (dead or alive).

The only thing that can kill a Ghoul is a decapitation or a complete destruction of the head.

Known Powers
Shape Shifting ﻿Ghouls have the power to transform into any human. This can only be done by eating a living or a corpse of a human being. Like Shapeshifters, ghouls also download the memories of the person they are mimicking.

Enhanced Speed ﻿Ghouls seem to move faster then typical humans. In the episode Two And A Half Men, after battling a monster in human form and move with super human speed, Sam listed down what creatures can move with supernatural speed; ghouls were first on the list. Sam and Dean learned later that they were hunting shapeshifters and the Alpha shapeshifter.

Enhanced Strength Ghouls are slightly stronger then humans. They can overpower a human, but can be fought off. Dean proved that he can fight ghouls even without using guns or other kinds of weapons. Ghouls are also not as strong as Vampires, Demons, Angels, and Archangels.

Weaknesses
Decapitation Complete removal or destruction of the head is lethal to a Ghoul.