An RP based on the TV show Once Upon a Time.
Basically it’s a show where Fairy Tale characters get sent to modern world due to a curse, and they don’t remember their fairy tale characters. It’s a rather complicated show, and I don’t know how it would work as an RP. Every character is connected to each other in some way, we would need a savior, a Dark One, a villain character to cast the curse, a couple to fill the role of Snow White and Prince Charming. Then there’s the question of how would flashbacks be handled, among other questions that I can’t think of right now...
It would be relatively easy to have each player sign up as a classic character from a fairytale, and then give them a modern alter ego as well. They'd outline both lives, the original history as well as the new "fake" one in our world, but their personality would be the same in both.
Then, I think the GM shouldn't reveal exactly how it came to be that they got stuck in the real world at the start. Likely, the GM would need to play the role of the one person who knows something is wrong. Either by a Henry type of character, or by somebody who comes from that world but has their memories intact. Perhaps there could be a magic or mechanics that will let this person convince the others one by one that they are actually from another world. This will likely only work if the GM sets up some events and has a plotline in mind that they somewhat linearly will follow... perhaps the GM can actually play several characters in the real world and not reveal to the players who they are in the fantasy world? So the players will know that one of them cast the curse and is the villain, but not exactly whom yet. And they have to figure it out :)
You could throw in flashback events just for fun, for a few characters at a time. Like how we saw characters meeting in unlikely situations in the flashbacks in the show, so that practically everyone knew everyone through someone in the end. And it could all build up towards the curse being cast and explained, and then jump forward to today and real world again and confront the villain.
Could be super fun if a GM (or several co-GMs) had loads of time and energy on their hands and hte players were motivated and devoted and didn't drop off ahah