In the season finale, Rumple told Regina and Emma that when the original dark curse in Fairy world was made, he took just ONE DROP of the potion and placed it on the parchment (The scroll Regina read from). Did we all noticed that when the same curse was used in Fairy World the color of the smoke was black and dark?? But on Earth/Storybrooke it's purple. Is it purple because magic on earth is unpredictable (like Regina said), or is it because it depends on the users intentions. hmmm???
Why Rumple didn't have to sacrifice Belle on Earth for the curse/magic to work? Because he used the whole bottle. In Fairy World , the curse (parchment/scroll) had only one drop which is the reason I believe she had to sacrifice her father.
Oh my god, AM I ONLY ONE ACTUALLY WATCHING THE SHOW?
That was NOT the curse. That was MAGIC. Gold outright states that he is bringing MAGIC into this world through the properties of the well combined with true love potion.