Rumple gets others to use magic so they have to pay the price. I do think as Rumple back in the early FTL he might have used and practice all the magical tricks but as he advanced in his knowledge he did not have to resort as often to these methods. I do not think Rumple believes Cora (as evidence by the look on his face) but it suits him to let her think that he believes her. Have you ever known Rumple to deal honestly and open with anyone?
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CORA uses magic all the time so she must be paying the price in someway… Maybe by the loss of her daughter’s love. We KNOW Cora has no heart… where it is hidden no one knows. Does Regina know Cora has no heart?
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