I’d like to think it was hearing his name, just for the sake of consistency with him remembering in the original Curse when he heard Emma’s name. Things happened pretty fast after she said his name, so it’s hard to say exactly what it was that triggered his memories.
Also: what’s a guardian? who’s a guardian?
a magical person maguffin so that Rumple has to stay the dark one and can become a shady villain when they need him
I’m with you on the magical person maguffin, and did roll my eyes because here we go again with another mythic sounding title for someone/thing that sounds so important they really should have been mentioned way before now if the writers weren’t just pulling something random out of their…hats.
But I think the actual purpose of it is so they can actually lay the Dark One to rest by the end of the season. The power won’t be passed on to a new Dark One, so they can really, properly close the book on Rumple. He can find a way to die, and also rid the world of the tyranny of there being a Dark One as well, thus having him achieve something heroic. The Dagger will still exist, so darkness will still exist, but as long as the Guardian has it, it can’t ever be used again.
That way, if the show ends, that myth of the Dark One gets resolved with a nice, neat bow on it. And if by some chance they end up with a season 8, they can have the new big bad steal the Dagger from the Guardian and try to use it.
As for who it is, I dunno, but surely Rumple sending Alice after Henry to stop him from changing the course of a particular story must have something to do with it.