@mujie I think the curse just affects people differently. The whole point of it is to take away everyone’s happy endings, and everyone’s happy ending is different.
Why wouldn’t the Wizard of Oz remember who he was? Regina remembers because she enacted the curse. Jefferson remembers because if he didn’t he’d be another rich, single guy living it up in a huge house. Rumple/Gold remembers because if he didn’t he’d also be another mean, rich guy living it up from “owning” the town. With their memories, they’re all just as miserable as everyone else. That could be part of the Wizard’s curse: To remember everything and not be able to find his own way home. It could be the reason he just came to town out of nowhere.
Regina wanted to control everything. The Dark Curse takes the bidding of that who enacts it. Yet why would Regina really want to put Oz through that? Why would she do that to Oz? I’d think it more likely to do that to the Queen of Hearts. The rules of Storybrooke seem to be that you keep your last personality from your previous life. The Mad Hatter was lost, and he stayed lost, 8 episodes after August appeared. He was still in Storybrooke. If August was lost, he would stay lost.