Board Thread:General Discussion/@comment-24304025-20150121190259/@comment-24674051-20150211020735

You know, worst case scenerio, they already have the Deux ex machina to accomplish bringing anyone back, or at least interacting with anyone. The wand that Rumple possesses is able to allow its user to cast any spell they have seen/experienced (TNPLH). Emma just happens to have been through the Time Portal (hence the whole frozen arc), and brought forward Marian. She could borrow the wand again at any point and cast the time portal spell.

I would rather they not use that, but it's already there, and needs no explanation. And of course, all Emma has to do is take Regina and Blue (and any other magic users) through the portal, and they will also be able to cast the spell using the wand. So much for limiting Time Travel. (Of course, all Magic, and ALL time travel, come with a price).