20. The Song in Your Heart

In the past, Snow makes a wish that grants the entire Enchanted Forest the ability to use the gift of song as a strength, which also spreads to Oz. When Regina becomes affected by the wish, she finds a way to end it before the first curse takes place, but the Blue Fairy, who granted Snow the wish, tells Snow and David that the wish will be part of Emma's destiny. In Emma's past, her chance to make use of her talent is held back by being told she'll be alone.

This would come back to haunt Emma in the present day, as Fiona use that weakness to take Emma's heart before unleashing a new curse on her wedding day, with help from Gold by freezing her family. Henry discovers a page in his book that reveals the song in Emma's heart will make her stronger, stopping Fiona from killing Emma. Emma and Hook marry before Fiona's curse erupts from the clock tower and spreads throughout Storybrooke.