When the Savior becomes the "Dark Swan," the lines between good and evil blur as Emma begins to relish the intoxicating taste of absolute power. Terrified she'll succumb, Emma and Hook visit Camelot to find the one person who may able to aid them: Merlin. Unfortunately, King Arthur proves treacherous, and when he joins forces with a vengeful Zelena, Emma and Hook's hopes are shattered. Now Emma and her entire Storybrooke family must embark on a chilling descent to the Underworld of Hades, where they'll try to rescue Hook from a fate far worse than death... with "help" from Rumplestiltskin. But will any of them survive the journey?
- Ginnifer Goodwin as Snow White
- Jennifer Morrison as Emma Swan
- Lana Parrilla as Regina Mills
- Josh Dallas as Prince Charming
- Emilie de Ravin as Belle
- Colin O'Donoghue as Captain Hook
- Jared S. Gilmore as Henry Mills
- Rebecca Mader as Zelena
- Sean Maguire as Robin Hood
- Robert Carlyle as Rumplestiltskin
- Main Antagonists: Nimue, Emma Swan, and Hades.
- Secondary Antagonists: King Arthur, Zelena, Captain Hook, and Cruella De Vil.
- This is the first season to have a different antagonist for the past and present storylines, with Emma acting as the villain in Storybrooke, while in Camelot the villains were Arthur and Zelena. However, Nimue and the Dark Ones are the true main antagonists of the season, with Nimue acting as the leader.
- The primary Disney movie basis for the first half of the season is "The Sword in the Stone".
- This season features every Big Bad, except for Tamara and Greg, Ingrid, Maleficent and Ursula, as well as Fiona, Lady Tremaine, Drizella and Mother Gothel, who were introduced later.