When Fiona gives birth to a baby boy, she and Malcolm are visited by their son's fairy godmother, Tiger Lily, as well as the Blue Fairy. Fiona and Malcolm are told by the fairies that their son is destined to be the Savior, but Fiona discovers from the fairy book of prophecies that her son is destined to die fighting against an unknown evil in an event known as the Final Battle. To protect her infant son, Fiona casts a ritual to turn herself into a fairy, so she can be powerful enough to create a dark curse that will diminish the prophecy's threat by sending it to a land without magic. Tiger Lily tries to stop Fiona, only for Fiona to rip her heart out, and it is this descent into darkness that transforms Fiona into the Black Fairy. After being banished to another realm by the Blue Fairy, Fiona uses her child slaves to mine enough black fairy dust to create the Dark Curse. Despite being trapped in her realm, she is briefly summoned by the Dark One, Rumplestiltskin, who paralyzes her with squid ink before interrogating her about the infant son she abandoned. At that moment, Fiona realizes Rumplestiltskin is her abandoned son, and laughs at his anguish before explaining that she chose power over love. When the squid ink wears off, Fiona leaves her son once again. Eventually, Snow White gets black fairy dust from her.
As the Blue Fairy is transporting Fiona's grandson Gideon to safety, she is ambushed by Fiona herself. After severely wounding her rival, Fiona abducts Gideon and takes him back to her realm, where she teaches Gideon magic and raises him as her son. However, when Gideon begins to rebel, Fiona rips out his heart so that he is completely under her control. She then instructs Gideon to kill Emma Swan so that her life force can be used to free Fiona from her own realm. Although Gideon fails to kill Emma, he manages to drain enough of her life force to open a portal that Fiona just manages to escape through. In Storybrooke, she confronts Emma and tells her they were destined to battle since the dawn of time. Fiona tries to ally herself with Rumplestiltskin and Zelena, but they both reject her offers. She uses Zelena's magic to corrupt the fairy crystals in the mines, but her plans fail when Zelena uses the Crimson Heart to destroy her own magic, destroying the dark magic in the crystals. When the Blue Fairy wakes up, Fiona kidnaps her so that her foe cannot divulge any secrets or information.
After torturing information out of the Blue Fairy about the location of a wand that can defeat Fiona, she tracks the wand down to Granny's Diner, where she finds the heroes have already found it. Fiona and Regina fight outside the diner, and Fiona nearly kills Regina, until Zelena runs Fiona over with her car. When Rumplestiltskin finds out that he was the Savior destined to kill Fiona, and that Fiona severed his fate with the magic shears when he was a baby before being banished, Fiona drops the bravado and speaks plainly with her son, telling him that she secretly still loves him truly. When Rumple returns from speaking with Fiona, he tells the heroes that he has banished the Black Fairy. In truth, however, he seems to be in league with Fiona, who tells him that Emma Swan will die on her wedding day, where Fiona unleashes a curse stronger than the Dark Curse. Under this curse, Fiona is mayor and tries to extinguish all hope and belief from Emma so that the realms of story will be destroyed. When she fails, Fiona forces Gideon to kill Emma, just before Fiona is killed by Rumplestiltskin.
- Black Fairy Magic: Fiona can use magic thanks to her black fairy dust, which fuels her power.
- Teleportation: She can teleport herself, as well as other people or objects.
- Telekinesis: Fiona can telekinetically move other people, as well as objects.
- Glamour: She can disguise herself as other people, such as Snow White.
- Heart-Ripping: She has the ability to rip out people's hearts to either kill someone or control them.
- Gideon (grandson /adoptive son)
- Henry Mills (great-grandson; via Baelfire)
- Emma Swan (Henry's mother)
- Cinderella Mills (great-grandaughter-in-law)
- Lucy Mills (great-great-grandaughter)
- Reul Ghorm (fairy)
- Tinker Bell (fairy)
- Silvermist (fairy)
- Nova (fairy)
- Tiger Lily (ex-fairy)
- Malcolm (husband)
- Baelfire (grandson)
- Milah (daughter-in-law)
- Belle French (second daughter in-law)
- Rumplestiltskin (son)
- While mayor of Storybrooke, Fiona was allegedly known for her infamous black pudding.
- The Blue Fairy kept the Black Fairy's wand, which was utilized during Peter Pan's attack on Storybrooke.
Behind the Scenes
- Fiona was the main antagonist of the second half of Season 6, although she orchestrated everything from the Dark Curse to the Final Battle between Emma and Gideon.
- S6, E09: "Changelings" (flashback)
- S6, E11: "Tougher Than The Rest" (flashback)
- S6, E16: "Mother's Little Helper"
- S6, E17: "Awake"
- S6, E18: "Where Bluebirds Fly"
- S6, E19: "The Black Fairy"
- S6, E20: "The Song in Your Heart"
- S6, E21: "The Final Battle, Part One"
- S6, E22: "The Final Battle, Part Two"
- S7, E10: "The Eighth Witch" (flashback)