Some films have so much story to tell that they actually feature multiple plots. While the main plot usually garners the most attention, the remainder of the film's screen time is devoted to less important storylines known as subplots.
Usually, subplots are subplots for a reason. They often don't hold a candle to the main storyline, and are there just to add a little extra flavour to the overall film. Many could be removed from the story entirely without affecting the film's primary story too much, and some lead to successful spinoffs in which the sub plot acts as the main storyline.
However, sometimes, sub plots outshine their film's main story. Often involving the most interesting side character, the most inspired story element, or the most thematically rich moment in the film, many subplots manage to become their film's defining features, rather than the main story.
While not every sub plot would work as the main story, many on this list would improve their films if they were more than just a subplot.
10. Gollum Vs. Smeagol - The Lord Of The Rings: The Two Towers
The second film in the Lord of the Rings trilogy might as well be called Gollum: The Movie. The new villain steals the show, becoming the first successful CGI character in film history, and, to this day ,one of the best. Many fans agree, even eighteen years later, that actor Andy Serkis should have been nominated for an Oscar for his revolutionary work.
Much of the charm of Gollum's scenes is the conflict between "Gollum," the creature corrupted by the One Ring, and "Smeagol," the innocent proto-Hobbit who found it. That divide drives the character, leading to incredibly memorable scenes, such as when he argues with himself on whether or not to kill Frodo and Sam.
Gollum vs. Smeagol is more compelling than the main plot of this Two Towers storyline, which brings Frodo and Sam to Osgiliath, a deviation from the books just added to the films in order to give the duo more to do. More focus on Gollum could have solved the problem far more effectively.