Thoughts about the faerie in fantasy games

I am really interested in faerie and how to use them in a gameworld. There really is no way to define what a faerie is however. Are they wild chaotic energy or are they whimsical spirits? There really is no clear definition. But one thing I have thought about is their origins. The elves, dwarves, trolls were creation or inhabitants of the Norse cosmology. The nymphs, fauns, dryads, centaurs and minotaur were from the Greek cosmology. The fomor and sidhe were from the Celtic cosmology. So this made me think that the true origins of fairies were from pagan cosmologies instead of some universal faerie land like Arcadia. So maybe when Christianity became dominant, the pagan religions were weakened but there were still creations of the pagan world roaming about. Maybe the reason that faerie tales tell of strange and fickle faerie is because the pagan creations (the faerie) were magical creatures that were un-aligned with either the Christian God or the Devil. They were free willed beings that had their own motivations and thus were unreliable or even chaotic to those of the Christian faith. What do you think? Thanks.

Thoughts about the faerie in fantasy games