I wanna say that the black sail is to do with the Shadow. But then what’s with the pixie dust?
Looking at the screenshot — I think Regina uses the pixie dust to imbue the sail with the shadow’s power to fly/travel
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Keeper of Hook and Emma's smoldering first kiss, a certain Pirate's sauciness, the Evil Queen's snarkiness, Grumpy's gruffness and a drop of true love to make it all go down smooth.