Source: Buffy the Vampire Slayer
Location: Unfortunately anywhere
Threat Assessment: 6. There seems to be a LOT of them. They are incredibly strong, fast, and have fangs. Some are more mystically inclined and have other supernatural powers.
Limitations: Need an invite to come into a house. Beheading or a wooden stake takes care of them and they turn instantly to ash. Also they don't have souls as a rule.