And what else has he collected that might be helpful?
I suspect the Crystal Ball orignally was his and then it was taken by Zelena. He showed her what was happening at that moment in the EF and we know the crystal ball can see into other lands.
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"I could have the giant duck as my steed!" --Daniel Radcliffe
Keeper Of Tamara's Taser , Jafar's Staff, Kitsis’s Glasses , Ariel’s Tail, Dopey's Hat , Peter Pan’s Shadow, Outfit, & Pied Cloak,Red Queen's Castle, White Rabbit's Power To World Hop, Zelena's BroomStick, & ALL MAGIC