I think you all are on to something with Blackbeard and Ariel as the way he gets to our world.
When it comes to who sends the message, I think Rumple or Neal. I know Hook somehow found them all at Neal’s building in Season 2, when he poisoned Gold. We aren’t completely sure that he knew Neal’s address and went there. He is a pirate from the EF, so understanding all about addresses would probably be a little complicated for him. This is why I’m thinking Neal sent the message & gave him some specific info. about NYC, since he knows it so well.
The other option is Rumple, since he obviously knew Neal’s NYC address. Also, he is probably captured by the witch & know’s her plans.
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