Donnie Darko
Donnie Darko is one of the most mind-bending films of all time. The plot of this film involves a number of complex timelines, events, and universes, not all of which can be condensed into a single coherent paragraph. In essence, Donnie had to die in the Tangent Universe to send the jet engine through a wormhole back to the Primary Universe. Time travel theory is extremely confusing, but there are plenty of resources to explore the topic more in-depth.