Origins of the Fey
The Dark Fey are a subspecies of Fairy, human in size and appearance however with large feathered wings and horns.
In Maleficent: Mistress of Evil, Conall tours and brings Maleficent around the cavern, describing it as their Nest of Origin. The nest is a large island, located in a remote part of the ocean far off of the coast of Ulstead.
The nest is a large landmass containing multiple 'biomes', those depicted in the movie are Tundra, Desert, Jungle and Caverns. These give variety to the Fey each of differing appearances. Young Fey are usually trained to fly from a cliff's edge inside the nest.
The origins of the original Dark Fey stem from the Phoenix mother, a large skeletal structure surrounded by fire and a dark clouded aura. Conall explains that this is the origin of all Fey, who evolved from the mother. Maleficent is a direct descendant of the Phoenix, which explains why her power is so immense to begin with.