Revealing mistake: When Nancy is running up the stairs in her house to escape Freddy for the first time her foot hits the steps and go through the steps into some goop. Look at the steps above that step and you can see the pre-cut holes where the next sets of goop will be. (00:39:10)
Revealing mistake: Trish jumps out the window and lands face up on the ground. You can plainly see it's Kimberly Beck's stunt double. She looks nothing like her. (01:21:35)
Revealing mistake: When the professor is trying to find the gremlin, he is in the room with the movie playing. The projector that is playing the movie is actually moving backwards. (00:44:35 - 00:47:35)
Revealing mistake: When Charlie sets the mens clothes on fire, burning gel is clearly visible on their clothes. (00:38:30)
Revealing mistake: As Vicky and Burt are driving down a dirty lane, through a row of corn, you can see fresh tire tracks in the mud from a previous take. (00:34:35)
Revealing mistake: When Melvin jumps out of the window, the person who falls out isn't actor Mark Torgl but a stunt double.
Revealing mistake: When Wilson crashes the truck towards the end of the film, you can tell it's actually a stunt driver because he has a full head of hair.
Revealing mistake: The robber who kills Billy's mother is shown cutting her throat but with the flat side of the blade. Moreover real blood doesn't ooze out so thickly, indicating it was makeup.