9. Star Trek: The Wrath Of Khan - Casket And Monologue
Star Trek II: The Wrath Of Khan famously features the death of beloved fan-favorite character Spock. This plot element had been leaked before the film's release, garnering a negative reaction. However, audiences weren't to know that decisions on the finality of this death had already been made behind the scenes. Leonard Nimoy, despite initially requesting the death, changed his mind, and this lead to the inclusion of the 'remember' moment with McCoy.
However, that wasn't enough for test audiences. They considered the film's ending to be too dark, despite the hopeful tone of Kirk stating he felt young again by the story's close. Harve Bennett listened, returning then to shoot two additional scenes. This included the reveal of Spock's casket on the Genesis Planet, and a final monologue, delivered by Nimoy.
The famous 'Space, the Final Frontier' lines play out before the closing credits. Combined, these elements effectively guaranteed a return for Spock, thereby ensuring a sequel was on the way. Director Nicholas Meyer was not a fan of these additions at all, but allowed them, believing the film strong enough to withstand them.