Celtic folklore — encompassing Irish, Scottish, Welsh, Breton, Cornish, and Manx traditions — provides a rich vein of supernatural creatures and concepts that Supernatural draws upon. The Celtic world is particularly rich in fairy lore, spirit traditions, and the concept of a thin boundary between the mortal world and the otherworld.
Changelings
The changeling is perhaps the most prominent Celtic contribution to the show. The concept of fairy beings stealing human children and leaving substitutes is widespread across Celtic traditions, with detailed beliefs about how to detect and counter changelings documented in Irish, Scottish, and Welsh folklore.
Fairies
Fairies appeared directly in Season 6, Episode 9, "Clap Your Hands If You Believe." The episode portrayed fairies as beings from a parallel realm (Avalon) who could be summoned through specific rituals. The show touched on the darker aspects of fairy folklore — abduction, time displacement, and the obligation to fulfill fairy bargains — while playing much of the episode for comedy. Celtic fairy traditions are vast and varied, ranging from the helpful brownies and household spirits to the terrifying host of the Wild Hunt.
Banshee
The banshee (bean sídhe) appeared in Season 11 as a creature whose scream could kill. In Irish and Scottish tradition, the banshee is specifically a fairy woman whose wailing foretells death — she does not cause it. Supernatural adapted the concept into a more active predatory creature while retaining the sonic element.
The Thin Veil
The Celtic concept of the veil between worlds — particularly thin at Samhain (Halloween) — directly influences the show's mythology. Supernatural explicitly references this in multiple Halloween-adjacent episodes and in its broader treatment of Purgatory and the afterlife as places that can be breached under the right circumstances.
Creatures from this Tradition
- Changeling - Parasitic creatures that replace human children, feeding on the mother's synovial fluid.