Copy/Pasted from Late June's Showdown:

This Showdown preys on the days of future past: the great and powerful films that came after the main event—whether that event was also a film, television series, novel, comic or song—and took us back to the beginning while continuing the story*. (*Reboots count only if they include otherwise unexplored origin stories.)

I've picked 10 movies that I think meet this requirement and are my personal faves of the bunch.