Back in the day when I was teaching people how to write, I used an exercise I called “Act Four” in which the students would write what happened after the play ended. It helped them connect with characters and look for ways to build a dramatic arc.
In a series of books, Dave Barry and Ridley Pearson flip that premise on its head and write about what happed BEFORE the story of Peter Pan. How does Peter and Captain Hook become mortal enemies? Where does Tinkerbell come from? How do the Lost Boys come to live in Neverland? And why does that alligator chase Captain Hook so diligently?