Plot hole: The TV-watching girl is killed when Freddy shoves her face first into a TV set. (one of the more creative movie deaths.) But the thing is, all the other deaths have been set up to look like suicides if not accidents - this one was obviously foul play, since there's no way she could have launched herself into the glass of a TV screen hard enough to break it. We see that her body is found this way, but they make no inquiry.
Suggested correction: Not all of the deaths were meant to be suicidal; Phillip and Kirsten were the only exceptions. When Will and Taryn were killed, it was in the dream when they wanted to help Kirsten but nobody was there to witness it and it was much later in the film. Also when Joey was caught by Freddy, he was only passed out but still alive. The one kid that cut his eyelids off was not only never shown but his death happened by his own doings out of fear for Freddy.
It doesn't matter if Jennifer's death wasn't intended to look like a suicide - she is in a locked ward and was the victim of a homicide. Yet there's no investigation.
Why would there be an investigation? Especially when she was the only one in the room - apart from Freddy - or maybe there were cameras there?
Plot hole: When Gallagher is trying to kill the senator at the end, he is fired on by his bodyguards. Yet when they finally catch up with him, they're quite content to stand back and watch him torch the senator. One of them even lowers his gun. They couldn't have known Gallagher and the senator were aliens. (01:27:20)
Plot hole: The army showing up at the end of the movie is wrong on numerous levels. 1) Eugene wrote and sent out the letter that day. I find it hard to believe the mailed letter got to the army in just a few hours time. 2) How did the army know to show up at time square? When Eugene wrote the letter, nowhere did it say where to meet. Plus the boys didn't decide to go to time square until the last minute. 3) since when is the army deployed to battle monsters based on a letter that was written by a child?
Suggested correction: The army's arrival being unrealistic is a very deliberate joke, like the armadillo-rats from earlier in the movie.
I submitted a category change to "Factual Error" to help cover this. It is indeed too deliberate to be a true plothole, but it is nonetheless amusing to point out all the ridiculous ways this humorous scene defies believability.
Plot hole: Why does the shark EXPLODE when it gets stabbed by the boat in the end? It had a transmitter of electromagnetic energy designed to shock it rammed down its throat, nothing that would explode like that.
Plot hole: After Blaine gets killed and the group hose down the forest, Poncho goes and checks for the enemy. He comes back and says he didn't find tracks or blood "We hit NOTHINGGG." Now, while he would be looking for red blood, he certainly should have noticed at least the glowing Predator blood (made from glow stick fluid - widely used by the military and public alike at the time) easily visible on the large leaf, and deduced that came from something - perhaps the enemy soldier had a glow stick.
Plot hole: The police are on the trail of a known psychotic and mass murderer. When they turn up at the house of the mother superior, it's evident Ricky has been there, as the door has been cut open and kicked in. There is no way the other nun would have been able to freely enter the house without police escort, or even get out of the police car, as Ricky had not been located and apprehended. The house is a potential crime scene and she would not have been allowed in.
Plot hole: In the morning at the motel, the vampires have a big shoot-out with local law enforcement, which results in one at least one cop being killed. But when they escape, the police don't bother pursuing them or even giving them a another thought. Even for an 80's film, this is beyond ludicrous.