Personally, I think any confusion is due to poor writing so that we have to try to make our own sense of what's going on. How many other shows have had to provide an hour-long introduction so people can get up-to-speed with the new season? Although I suppose more ought
to provide a similar intro
Remember that the basis for magical strength in this NeverLand seems to be belief. If you believe you can do something, you can. When he was made young again, he believed more strongly.
There's more than one Shadow. (Remember that Rumple cut free his own NeverLand Shadow to hide his knife.) Whether or not the Shadow which gave Pan his original powers was his own Shadow isn't clear to me, either. Maybe he left it behind when he first visited as a child. Maybe it's someone else's shadow. Or maybe it's a magical entity which is the real basis for NeverLand and is just pretending to be a Shadow. And maybe Pan lied about it being his
Shadow. We know he's a con-man.
I have to admit that I'm somewhat annoyed that they're making everything be based on feuding among members of a single family.