Seriously speaking, that would be mind blowing, marketing a movie as, let's say, a romantic comedy, and make it so for the first 30 minutes, and then BANG the major character in the movie goes postal and the whole thing becomes Rambo, then there's like, NO romance and 90 minutes of violence and gore, and explosions.
Or a movie like Dinner with Andre, have you seen this? 2 hours of the two characters talking philosiphically, imagine how cool it would be if one of them killed the other and spent most of the movie trying to get rid of the body, I mean, mind blowing, if you market it as if it's just a talk movie...