I'm not sure how I feel about all the DOs coming back as it seems they'll have magic. It makes sense if they had magic power before becoming the DO (like Nimue), but individuals with magical powers do not seem that common so it doesn't really make sense to have all of them being magically powerfull.
There are no sign so far that Rumple has retain his magicial power let-alone his knowledge although I think he could make potions and stuff but simply wants to stay as far as possible from it which would explain why Merlin was able to make that voice-mail-dark-curse-ready cauldron after loosing its power.
When modifying the curse, Emma took the memories from maximum 10 persons, yet her garage was filled with dreamcatchers. Why in hell did she needed to take away so many memories after the curse was completed? Or are they simply the manifestation of the memory lost of everybody who was included in the curse?
Eventhough Emma took Hook's memories away how could he not hear Excalibur calling him? I guess they'll trow an easy line at some point where Hook says he felt weird whenever around Emma's house...
And again, concerning that curse, how fortunate was Hook to have that cauldron ready with only 1 ingredient missing to cast the curse... I thought Merlin was a real deception thus far this season but I think the Dark Ones are up for a masterclass of what making a big-ass plan is all about. I wouldn't be surprise if Merlin was able to come to Storybrooke using that Underworld boat.