Leprechaun

A leprechaun is a non-existant fictional being, similar in legend to a skench demon. (ATS: "Double or Nothing")

In 2002, Andrew Wells compared Jonathan Levinson to a leprechaun, based on his height. (BTVS: "Seeing Red")

In an attempt to hide her identity, Eve jokingly stated she was a leprechaun from Brigadoon. Spike had heard this claim several times before 2004. (ATS: "Underneath")
 * The fact that leprechauns don't exist was also mentioned in the ATS episode "Unleashed" by Crane.