9. Harry Potter And The Prisoner of Azkaban
Theres a reason you never involve time-travel in stories not ostensibly about that particular subject it can absolutely ruin audience participation in your film, because theyll be left wondering why they couldnt just break out their cure-all plot device when things get hard. In a standalone film its bad enough, but when your film evokes time-travel midway through the canon, youre asking for trouble. Its a shame, because taken by itself the finale to Prisoner of Azkaban is very clever, explaining all the unseen, seemingly Deus Ex Machina moments that happened to the Potter trio at crucial points. However, if taken as part of a complete whole, you have to acknowledge that its ill-advised at best. Theres a reason why J.K. Rowling wrote out the time-turner technology in Order of the Phoenix it was just too much of a headache. After all, the time-turners couldve nullified Voldemort in Book 4 if Hermione were to grab Dumbledore and turned back time after Harry came back with a dead Cedric Diggory, the omnipotent headmaster couldve pulverised Pettigrew and put the stunted Voldemort in a box somewhere where he couldnt bother anyone. Its all pretty simple, really, and it's a Pandora's Box unleashed by Azkaban's final act.