So this last week was pretty easy to identify and OMG was it completely on point with where the season arc was and what happened in this episode.
S3 E17: The Law of Sacrifice
“The queen was terrified and offered the little man all the riches of the kingdom, if only he would leave the newborn child alone.”
Definitely Rumpelstiltskin - and even with the giant heads-up this quote gave us, the episode still had a really fresh take in using the tale. Whoever says the show isn't using fairy tales so closely hasn't been watching. They're often more real-world integrated than those of OUAT or retellings.
EDit: Oops - posted this in the wrong place initially. Apologies.
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