In Oz, Glinda asks Zelena to be on of the sister witches. She would be the keeper of innocence. Glinda gives her the pendant to heighten her power but if she removes it she will lose her power.
Zelena accepts but then envies Dorothy when she arrives, believing that she can take her power and that her own destiny is one of evil. She tricks Dorothy, then sends her back to Oz and banishes Glinda.
In Storybrooke, Zelena drowns Hook so that Emma can only save him via mouth to mouth resuscitation. As soon as their lips touch, she loses her magic.
Snow has a baby boy and Zelena steals him. He is the innocence she needs to cast her spell. But Regina stops her when Henry convinces her she can use light magic to win.
Later, Regina chooses to let Zelena live. She locks away her pendant and puts her in jail.
Belle gives Rumpel back his dagger but he gives it back to her and asks her to marry him. She says yes. Little does she know that Rumpel slipped her a fake dagger. With the real one he secretly kills Zelena in her jail cell. Afterwards, her pendant turns to green mist and travels through the town to the place she tried to cast her spell.
Emma happily meets her baby brother but Hook is heartbroken when she tells him she plans to take Henry and move back to New York.