Yes, I think Hades is probably the one who created the Dark Curse. When you boil it down to its basics, the Dark Curse takes away Happy Endings, the very thing that Emma restores. I think Hades and Emma are being set up to be opposites of each other (the enemy of life, the savior or life;) It would make sense for him to have created the Dark Curse that she was destined to break.
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"He was a lot of things to me" "The only conclusion was love"