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)
Continuity mistake: When Trish and Tommy push the cupboard in front of the door, the figurines and items on the shelves move/fall off/reappear between consecutive wideshots and closeups. (01:15:10)
Visible crew/equipment: When a gremlin attacks the Mum from a Christmas tree, and the tree falls on top of her, you can clearly see a member of the crew with eyeglasses, wearing a red shirt, standing behind the tree pushing it forward on top of her. (00:54:30)