9. What Happened To The Symbiote? - Spider-Man 3 (2007)
Sam Raimi's infamously panned third Spider-Man flick is a kind of mash-up of storylines that never quite gelled properly, one of which concerns an alien parasite that comes down from a meteorite, attaches itself to Peter Parker and transforms him into an emo. Eventually Parker manages to kick the symbiote like a nasty drug habit, but it finds itself attached to Topher Grace. By the end of the movie, Topher Grace (as Venom) is defeated, and the Symbiote... well, it gets away.
We know this because we see that some of it has found its way into Dr. Connor's laboratory during the course of the movie. You might argue that since Sam Raimi planned on making a fourth Spider-Man and never got around to it, it was intended that the conclusion to the Symbiote storyline would be continued admist that movie. That never happened, of course, and the series was rebooted with some fresh news faces, meaning that - in our minds, at least - the Symbiote ran wild and eventually destroyed New York City.