Mary Lydgate is an episodic character on Once Upon a Time. For years she was the object of desire for Dr. Jekyll, but she found his other half far more preferable, which didn't end well for her once Jekyll learned the truth...
Before the Curse
Mary takes a fatal fancy to Mr. Hyde. ("Strange Case")
Mary spends years in the company of one Dr. Henry Jekyll, who pines after her all this time. She eventually sets up a meeting between Jekyll and her father, Dr. Lydgate, in order to give the former a chance to showcase his serum which, once completed, should be able to separate a man's good half from his evil half. Lydgate, however, dismisses Jekyll's work as being dangerous, and refuses to grant him membership to the academy like he's always wanted. That night, a party is held in the Lydgate home and Mary and her father are met by a stranger named Mr. Hyde, who claims to be a friend of Jekyll's. Mary is rather obviously interested him, and he successfully intimidates Lydgate into handing over an academy pin for Jekyll. The next night, Mary is approached by Mr. Hyde as she's walking home, for he has been sent to tell her that Jekyll has very strong feelings for her. She makes clear that she cares deeply for Henry, but she could never be with him in that way, the reason being that he sees things such as passion and desire as contaminants to be eliminated... but she needs someone who wants to bathe in passion and give in to desire, and she has a feeling Hyde knows what she's talking about. She then kisses him, proceeding to take him to bed with her, and the next morning he wakes up - as Dr. Jekyll. Mary grows deeply confused but soon comes to understand that Hyde was in fact Jekyll's alter-ego as a result of the serum, and she refuses to ever love the doctor because he's weak and completely mad. This enrages him enough to engage in a struggle, which ends tragically when Mary is pushed from her bedroom window to her death. ("Strange Case")