Ok. I’ll jump on this and see where it takes me. If it makes no sense, it’s cause I’m just typing.
The Shadow, we’ve theorized in other places, might be a part of the Dark One. A piece of the Dark One broke off during The Return and came to A Land Without Magic AFTER it had gone to NL. This might explain why Rumple was never as Dark as he could be.
While in NL, the Shadow was put under the control of Felix. So when the cast get on the JR to go to NL, part of Rumple is already there and being controlled by Felix, who looks pretty sinister to me.
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"He was a lot of things to me" "The only conclusion was love"