Jacques Vallee Reveals the True Nature of Aliens and Fairies
Jacques Vallee, a well known UFO researcher, wrote in his book Passport to Magonia that from ancient times people have described encounters with fairies that seemed to have intercourse with human beings. Vallee compares demons with fairies in the same book:
"What we have here is a complete theory of contact between our race and another race, non-human, different in physical nature, but biologically compatible with us. Angels, demons, fairies, creatures from heaven, hell, or Magonia: they inspire our strangest dreams, shape our destinies, steal our desires......
But who are they?" 
The Bible reveals how a third of God's angels rebelled against Him, and became fallen angels that served Satan, who had been known as the angel Lucifer. Revelation 12 speaks of a great red dragon (Satan) who drew a third of the stars of heaven.
Revelation 12:3-4 a.
 And there appeared another wonder in heaven; and behold a great red dragon, having seven heads and ten horns, and seven crowns upon his heads. [4 a.] And his tail drew the third part of the stars of heaven, and did cast them to the earth: ..."
Isaiah 14:12 speaks how Lucifer (Satan) is fallen from Heaven. The prophecy says: "How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations!" In Luke 10:18, Jesus said that He saw Satan fall from heaven. Luke 10:18 — "And he said unto them, I beheld Satan as lightning fall from heaven." Revelation 12 goes on to say how Satan was cast out of heaven with his angels.
Revelation 12:9 — "And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him."
These same evil spirits go forth seeking whom they may devour.
1 Peter 5:8-9
 Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:  Whom resist stedfast in the faith, knowing that the same afflictions are accomplished in your brethren that are in the world.
These evil spirits can appear as angels of light to deceive men. 2 Corinthians 11:14 — "And no marvel; for Satan himself is transformed into an angel of light." They are deceivers and liars that make themselves appear like what they are not. If demons can appear as angels of light, why can't they appear as fairies, elves, leprechauns, dwarfs, trolls, monsters, dryads, nymphs, aliens, etc.?