Continuity mistake: Dewey removes a VHS from the VCR. The VHS has a black spine. A minute later they begin getting jiggy with it and in the shot from the front of the desk (the rear view of Mrs. Cox, if you prefer) you can see on the VCR a white label on the spine. (01:17:10)
Continuity mistake: When Dewey and Gale are in the classroom and as they are making out, when they realise that they are being filmed, Dewey has one side of his jacket off below his shoulder and in the other camera angle it shows that he has it perfectly on. (01:18:50)
Continuity mistake: Courteney Cox's right hand is alternatively on the horizontal shelf or the vertical bar of the archive when Dewey tries to warn her from the other side of the glass. (01:21:45)
Continuity mistake: When Dewey is trying to get Gail's attention on the glass, his hand changes from being open palmed to a fist, between shots. (01:21:50)
Continuity mistake: The amount of blood on Dewey's forehead at the very beginning of the scene of his 'death' changes between shots. (01:21:55)
Continuity mistake: When Gale watches Dewey agonize behind the glass, her hand is in different positions and spots between shots. (01:22:15)
Continuity mistake: In the sound room murder, Gale stares at Ghostface from the other side of two different bloodstains on the glass. (01:22:30)
Continuity mistake: When the killer attacks Sidney and the bodyguards in the car, he smashes through the driver's side window, leaving some of the glass still around the edges. When the killer drives off, these fragments have dissapeared and the window is totally gone. (01:22:40)
Continuity mistake: At the dorm, Sid and Allie hop in the cop car with Sid in the left backseat and Allie in the right backseat. In the following scene they have swapped. (01:24:25 - 01:25:50)
Continuity mistake: When Sid and Allie start freeing themselves from the wrecked police car, the metal pipe left a tiny hole in the grid, which is immediately larger in the next shot. (01:28:15)
Continuity mistake: When Mickey shoots Derek, his bandage touches the ropes, but both before the gun fires and when Sidney cries out and steps closer, there are a few inches of distance between bandage and rope. (01:37:10)
Continuity mistake: When Gale is in the theatre and gets shot and falls from the stage, she has blood stain on her left breast (above the place where the shot wound appears). Yet later, when she climbs back to the stage, she has no blood stain, only the shot wound. (01:37:20 - 01:45:45)
Continuity mistake: When Derek dies after being shot, tied up on the stage prop, his head slumps down with it looking down to his right towards Sid with his forehead tilted to the left. When it cuts to another angle at a close up of Sid, suddenly his head is tilted the other direction. (01:37:40)
Continuity mistake: Mickey and Sid at the beginning of their struggle end up facing each other with a Greek pillar between them. The position of their hands changes between shots, literally touching at some point depending on if Olyphant's hand is higher or lower. (01:39:25)
Continuity mistake: When Mickey grabs the gun after the 'pillar fight', he holds it straight in the first shot, gangsta-style sideways in the next. (01:39:35)
Continuity mistake: When Sidney incredulously asks "Mrs...Loomis?" her left hand is raised at shoulder level, but her arm is straight in the next shot. (01:40:20)
Continuity mistake: When Debbie Salt is holding the knife on Sidney, the knife changes positions from time to time. (01:42:30)
Continuity mistake: During the struggle between Debbie and Sidney, in the phase that involves the fake stone block Sidney's hands have a different position on the block between shots, and so does the knife, stuck in it in different spots. (01:46:10)
Continuity mistake: When Sidney and Mrs. Loomis fight with the knife, the weapon is bloodstained in different ways depending on the camera angle. (01:46:20)
Continuity mistake: Cotton shoots the killer, who when lying down has a giant hole in their throat. It wasn't there when both the killer and Sidney were falling backwards. (01:48:40 - 01:49:05)
Answer: His main motive was fame, or infamy for that matter.