Revealing mistake: When the killer is attacking Cici on the balcony, you can see blood on Cici's back before she is even stabbed and both times she is stabbed, the knife that comes out of her back has no blood on it. (00:33:20)
Revealing mistake: Just before the cop gets impaled through the head by the pole, you can see that it is obviously a dummy. (01:23:45)
Revealing mistake: In the opening scene when Phil gets stabbed in the head, watch carefully and you can see the retractable blade popping back out when he pulls his head away. (00:08:05)
Revealing mistake: When the killer attacks Sid's bodyguards, the younger one has blood on his throat before the killer slashes it.
Revealing mistake: When Cici is stabbed in the sorority house, her shirt is bloody, but there is not a hole in the material. (00:33:20)
Revealing mistake: When Randy, Gale, Dewey and Joel are sitting on a bench in the school grounds, Gale is smoking; but no smoke comes out of her mouth when she takes a drag. (00:58:35)
Revealing mistake: When Mickey is flying through the air after getting shot at the end of the movie, if you look closely you can see it's a stunt double. (01:46:00)
Revealing mistake: When Mickey draws the gun at the end of the movie, a hammer is heard being pulled back. Yet the gun that Mickey is using is hammerless.
Revealing mistake: When the killer kills Hallie you can plainly see the stuntman's eyes through the mask eyeholes. (01:32:00)
Revealing mistake: Towards the beginning, when Gale Weathers is talking to the sheriff who is standing at a podium, you see Mickey filming her with a hand-held camera. A panning shot going right following Mickey with some friends walking sideways reveals him looking at the camera twice. This is because he was waiting for his cue to stop. (00:20:50)
Revealing mistake: At the start when Phil Stephens is being stabbed, when the killer draws back the knife you can see there is already blood on the knife. Its only there for a second so you have to look carefully. (00:07:45)
Revealing mistake: When Mrs. Loomis dislodges the knife from the stone and lunges towards Sidney, the person falling back is not Neve Campbell, who comes back for the close-up shots. (01:46:15)
Answer: His main motive was fame, or infamy for that matter.