That’s a great point, Jo, and that occurred to me after I posted. It could be Henry PP is really after, but he also wants Rumple and Emma. The Dark One and the Savior.
I like that! It implies that PP needs the combination of dark magic and light magic. Plus, Henry is the combination of magic and non-magic since he is a child of parents from a land with magic who was born in a land without magic.
This whole yin/yang idea could also tie in with the shadow; perhaps when the shadow is ripped from a person, all of the evil within them is isolated in the shadow. If PP has been collecting shadows for centuries, he could be really bad!