Supernatural (2005)

Season 6: Episode 9

While Sam and Dean are investigating a UFO sighting, Dean is abducted from a crop circle. However, when he awakens, he discovers he isn't dealing with aliens, but fairies! Unfortunately, only Dean can see the fairy that keeps attacking him which makes tracing and stopping them difficult. The brothers become even more perplexed when Sam's investigation leads them to a world full of elves, gnomes and a leprechaun.