Revealing mistake: Melina is supposed to have been killed in the fall at the party, yet in the final version of events shown she displays signs of life right up to the moment her body is disposed of at the building site (twitching closed eyes, chest rising and falling from breathing, neck pulsing, etc).
Revealing mistake: When Phil kills himself by throwing himself off the roof, in the shot of him supposedly hitting the ground it is painfully obvious that it is a dummy. Not only does it hit the ground completely rigidly but the wig on it even noticeably flies off on impact.