The Fairies of Luna are girls who were turned into sprites by Moon and her unicorns and nightmares. If a girl was kidnapped by an unicorn, he will turn her into a fairy of blessing and miracles, but if it was a nightmare, the mare will turn her into a dark fairy of curses and spells
Those fairies are spirits of blessings. They love to bring smiles on sad people and to make old people younger. Many people sleep on open field gardens during Full Moon to make easier the visit of those fairies. The side-effect is that those persons may be visited by not-so-welcomed sprites, like nightmares and dark fairies, who can bring the terrible spirits of Night on them.
Dark Fairies are spirits of spells and enchantments. On Full Moon, they incite people to cast enchantments upon each other, revealing them even the most terrible lunar spells. They usually love to turn women into enchantresses, seducing them to use the dark arts of Night to get any purpose. They are usually invoked on Full Moon ritual by young enchantresses who want to get revelead the secrets of the Moonlight.