Board Thread:Spoilers!/@comment-5899967-20170224112659/@comment-1916997-20170224170830

Walecs wrote: "The darkest soul we’ve been teasing for six years" The Black Fairy has only been mentioned in season 3, thus she's been teased for 3 years at max. Like Esk said, it has been confirmed that the Black Fairy is who Snow got the dark fairy dust from, meaning she was indirectly mentioned in Season 1. The lines we're (doing from memory, so I'm paraphrasing):

Snow: I've got some fairy dust that will turn my enemies into a form that's easy to squash.

Charming: I thought fairy dust was good.

Snow: It is, if you get it from a good fairy.