Revealing mistake: As the Phantom traps Shaggy and Scooby in the room full of tables, he picks up a meat cleaver and starts chancing them. He swings it the first time and hits a table in a close up and cuts the cloth on it. Then as he is chasing them around, he leaps over one table and slashes down, having a heavy impact with the cleaver on another table. But when he lifts it up, there is absolutely no damage left to the table or cloth.
Revealing mistake: As the gang is watching The Phantom on the security monitors, he turns around and takes off down a hall. The only lights in the hallway are suspended from the ceiling in the center. Yet the Phantom's shadow is cast to his right on the wall, when there are no lights to his left.