Other mistake: There are several moments while using the clown dummy toy that make it very obvious it is an actor in a suit. Most obvious of which is that it somehow 'senses' things like the momentum and orientation of the person controlling it, when all it is shown to do is copy muscle movements/motor skills. There are far too many examples to list.
F/X2 (1991)
1 other mistake - chronological order
Directed by: Richard Franklin
Starring: Brian Dennehy, Bryan Brown, Rachel Ticotin, Joanna Gleason
Revealing mistake: When Rollie is hanging from the ladder and the bolt breaks, you can see the smoke from the exploding bolt. (00:42:50)
More trivia for F/X2