Continuity mistake: In the grave yard, Binx is sitting on the book so Winnifred can't get it. A second later after their exchange, the cat is suddenly missing.
Revealing mistake: Right before the witches burst through the roof of Max's house, after they retrieve the book, you can see the charge used to set off the explosion in the window just below where they exit.
Other mistake: Winnie could not have known that Max said, "It's just a bunch of hocus pocus," considering the three of them were still dead at that time. (They couldn't have been ghosts, because she didn't know who lit the black-flame candle.)
Other mistake: When Sara lures Emily to the Sanderson house with her song, Emily is laughing and running even as she enters the house. Later in the movie when Sara lures the town's children to the Sanderson house with her song, they were all in a hypnotic sleepwalking state.
Suggested correction: The difference is that Sarah was interacting and playing directly with Emily whereas she only cast the spell over the other kids from high above.
Other mistake: The same footage of Allison making the salt circle in Max's room is used both times we see her do it.
Revealing mistake: As Mary flies toward the kids in the cemetery, the wires holding her are visible.
Continuity mistake: As Alison holds off the Sanderson sisters with the box of salt, some shots show her holding the salt up close to the Sandersons while other shots the box of salt Is further away from them.
Continuity mistake: When the sisters are in "Satan's" house and meet the wife, her curlers change position.