Board Thread:Spoilers!/@comment-27060727-20170218051023/@comment-31231929-20170323021924

I've had this theory that the Black Fairy is actually the evil half of Blue. This could be because when we are first introduced to Blue, she is called Reul Ghorm and Morraine says she is the ancient being that rules the night and is the original power. Now, the Black Fairy rules the Dark Realm where it is probably constantly night, which fits the ruling the night part. The original power could mean that Rheul Ghorm is the oldest magical being in the Once-verse. Another thing Morraine mentioned was that she was bigger than anything which points to her also being the most powerful. From what we know of Black's history with Blue, Blue overpowered Black, took her wand, and banished her to the Dark Realm. From what we've seen of her, Black is extremely powerful so I would imagine that her and Blue are fairly evenly matched. From what we know of a split person, the good half can retain some of the darker qualities of the evil half. Blue is often seen as being shady and one of the descriptions that Rumple gives of the Black Fairy is that she "lurks in the shadows." Adam has also said that the Black Fairy's introduction has been teased for six seasons. Whether this actually pans out or not remains to be seen. However, I think it would be really interesting if it did.