I know that it may be a bit late but here are my two cents on the mad hatter theory.
So Regina sends Cora away, we can presume Wonderland. Cora becomes queen of hearts.
Somehow Regina's father ends up in Wonderland as a captive. Regina sets out to rescue him. Leaves poor hatter there.
Hatter goes mad probably trying to make another hat so that he can go back but that doesn't happen. Until, perhaps, Alice comes. They somehow banish the Queen of hearts back to that unaffected corner of the land. Alice returns to her world and the mad hatter with her. That would explain how he had his past life memories and how Regina didn't know his identity in Storybrooke.
I love the start of season two. Great writing. I was worried how they would continue the storyline and still make links to their old land. But the new storyline direction exceeded my expectations ten fold.
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