Saw
Many fans believe that the first movie in the Saw franchise is also the best. The film ended with two reveals—Zep, the implied mastermind behind it all, was blackmailed into working for Jigsaw. Secondly, the body in the middle of the bathroom was very much alive, eavesdropping on Dr. Gordon and Adam as they uncovered darkest secrets. Oh, and the "body" was none other than Jigsaw himself.