2. Alien
Believe it or not, Ridley Scott wanted to end Alien with the Alien biting Ellen Ripleys head off. The Alien would then make a log entry in Ripleys voice, presumably setting up a sequel in which it would menace another hapless crew. The producers found this idea to be far too dark and insisted that the Alien must be killed. Thus, Ripley lived to battle aliens another day and Sigourney Weaver earned an Oscar nomination for her performance in the second film. Now for those of you expecting a snarky comment about Prometheus, Im one of the few people who havent seen the movie so it wouldnt be fair for me to bash something I havent seen. Sorry.