I’m thinking the real big bad won’t be the Witch, it will be Oz. They could potentially make Oz into a very cool villain. Remember the way they ask who casted the curse in the trailer? I think they’ll discover the witch’s “Wicked” motives are a lot more sympathetic and she’s actually working to undo whatever Oz is. I can see Oz being part of some group of Fairy Tale illuminati along with the Dark Fairy(and the Blue Fairy at some point). The illuminati is more good than evil initially but gets corrupted. It will be something to do with who wrote Henry’s book, where the Dark One comes from, why classic fairytale characters exist “parallel” instead of centuries ago etc.