Silver Slippers are a pair of magical silver shoes, that when clicked three times at the heel, will transport the wearer to another world. Zelena uses them to travel to the Enchanted Forest, and Dorothy Gale uses them to travel back to Kansas.
Before the Curse
Zelena is given the slippers by the Wizard.
Zelena grows up in Oz, but her mother eventually passes, and so she is left with her unloving father. When finally learning that they are not her biological parents, Zelena flees, heading to the Wizard of Oz in hopes of finding a family who loves her. She is told her heritage, and soon learns of a half-sister, Regina, she has, one of which she quickly becomes envious of. The Wizard gives Zelena a pair of silver slippers though, and she is able to travel to the Enchanted Forest where she meets Rumplestiltskin. Knowing that it's Cora's daughter who must cast the Dark Curse, the Dark One takes Zelena on as a student, but with her jealousy for her sister and her love for her teacher growing, Rumplestiltskin is forced to drop her. She then uses the slippers to return back to Oz. ("It's Not Easy Being Green")
Dorothy used the slippers to travel back to Kansas.
When Dorothy Gale arrives in Oz via cyclone, Zelena fears that the young girl is prophesied to defeat her. To prevent this, she tricks Dorothy into thinking she's killed her and then she poses as the Wizard of Oz. She gives her the silver slippers so that she may travel back to Kansas. The Wicked Witch then banishes Glinda to a pocket dimension, allowing her to rule over Oz alone. ("Kansas") Rumplestiltskin, wanting the silver slippers to travel to a land without magic, sends Jefferson to Oz to retrieve them. However, he returns empty handed, as the slippers already traveled realms with Dorothy. ("The Doctor")
Dorothy hears from the munchkins that Zelena is back and ruling Oz wickedly, and so she uses the silver slippers to return and challenge her, believing she has the love of the people on her side. ("Our Decay")
After the Curse
Dorothy retains the slippers and is wearing them when she meets Ruby and Mulan in Oz. However, a cyclone soon hits and Zelena returns, having been banished by her sister Regina. She discovers Dorothy's dog, Toto, amid the wreckage and she kidnaps him, using him to ransom the slippers from Dorothy. Eventually, Dorothy goes to confront her with sleeping powder only to be hit with a sleeping curse instead, and Zelena robs the slippers from her unconscious body. ("Ruby Slippers")
Red and Snow use the slippers.
Zelena plans to leave the Underworld using the slippers after Ruby arrives looking for her, needing a way to wake Dorothy, but she's stopped by Regina and the rest of the heroes and made to hand the slippers over as an early act of redemption. Later, Ruby uses the slippers to return to Oz and wake Dorothy with true love's kiss, and then she uses them to drop Snow off home in Storybrooke to reunite with her son. ("Ruby Slippers")