I think Pan didn’t really bother with Regina because he didn’t consider her that much of a threat. Pan’s a guy who gave up his own flesh and blood child, so how could he possibly comprehend that someone could be a parent with unconditional love for a child they’re not blood related to. So that moment when Regina used her unconditional love for Henry to break free of the tree and put some serious smack down on Pan, he was completely unprepared for her. And I think now that he’s in Henry’s body, he’ll be out for some revenge against mummy dearest.