Revealing mistake: In the shot of the whole band in the trailer, Freddy's and Bonnie's mouths clip through their body.
Revealing mistake: In Foxy's jump scare, his ear clips through the top of the door for the first few frames.
Plot hole: According to the Lore, Purple Guy hid in a Spring Bonnie suit to lure the kids into the room he would kill them in. This is a continuity mistake as well as a plot hole because the plausibility of the disguise is highly diminished when the Phone Guy tells you that the suits kill people when they get stuffed into them on Night 1.