After having to abandon her child, leaving him with the father, Fiona changes and instead of helping children, she begins abducting them. 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 flees 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.
- 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.
- Malcolm (deceased ex-lover)
- Rumplestiltskin (son)
- Gideon (grandson/adoptive son)
- Baelfire (deceased grandson)
- Henry Mills (great-grandson)
- Milah (deceased daughter-in-law)
- Belle French (second daughter-in-law)
- Reul Ghorm (fairy)
- Tinker Bell (fairy)
- Silvermist (fairy)
- Nova (fairy)
- Tiger Lily (ex-fairy)
- The Blue Fairy kept the Black Fairy's wand, which was utilized during Peter Pan's attack on Storybrooke.
- 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"