Board Thread:General Discussion/@comment-25536775-20170510235618/@comment-25926288-20170511014244

I would say that it's due to the fundamental question "How does the curse work?"

This "Dark Curse" is just black fairy dust (aka a bunch of generic dark magic). The one of Fiona's past was a bunch of stuff and wolfsbane. The one Hook cast had a voicemail spell and a heart. Regina and others had the fundamental ingredients (dark souls' hair, etc) and a heart.