Black Swan
Natalie Portman and Mila Kunis play rival ballet dancers with a strange connection that is only revealed toward the end of the film. After Nina (Portman) stabs Lily (Kunis), she steps on stage to dance in Swan Lake—only to realize that Lily was a stress-induced hallucination, meaning Nina has actually stabbed herself. Although Nina's fate remains a mystery, she certainly gave the performance of a lifetime.