Just wanted to throw this out there as idea.
What if the Shadow is the power behind the Dark One?
I mean the Dark One would have to have a start at some point and someone had to make those rules and the Dagger that can kill him.
So what if this Shadow has been behind Rumpy getting power, the curse happening etc. What if this Shadow has been pulling the strings this whole time and giving Rumpy the nudge at the right times to do everything that he been doing?
Cause for some reason we have Rumpy and Regina together on a boat. So thinking its them 2 against the Shadow, magic vs magic.