Plot hole: This huge demon monster flies around and is seen by at least 30 people, and the day after this demon kills all these people. Everyone just goes on with their daily life. Where the hell is the FBI and the National Guard, this thing just killed 10 people and there's no search the next day for this demon that killed about 5 police officers?
Other mistake: When Darry is in the basement under the church, Darry is laying on the floor surrounded by a circle of sunlight appearing through the pipe. Then follows a series of cuts between Trish at the open end of the pipe, and Darry. Why do we not see a silhouette of Trish on the floor rather than a perfect circle of light?
Continuity mistake: The police station that they stop at is in a very out of the way rural community with only a few people in the jail. However, once the demon enters the jail and the alarm is sounded there are at least 20 cops on duty - all at the station in the middle of the night, in the middle of nowhere.
Continuity mistake: There are at least two different 1960 Chevys used in this film. There is a noticeable difference in the front bumpers. Notice the front bumper area just below the headlights. The first car used has a plain straight bumper, the second one has little chrome trim riser mounted just below the center of the headlights. The second one first shows up at the cat lady's house. The lower tag pan also changes.
Continuity mistake: When the main characters visit the house of the old woman with the cats, she comes out and aims at the monster with a double-barrelled shotgun, and fires one shot. Then when she goes back into the house, two shots can be heard in quick succession. She must have re-loaded the empty barrel quickly...
Other mistake: After the creature flies out the barred window with Darry, you see some bars missing from the earlier intact window, but where some of the bars are missing, there are intact bars surrounding it. The creature couldn't make a hole in two different places while flying out.
Plot hole: Since when do hell-born freaks have an intuitive knowledge of mechanics? And where did he get the turbo engines and various add-ons needed to reach such high speeds? It's a small rural area and it would look pretty odd if he just strolled into an auto shop and piled the stuff into a trolley.
Plot hole: The whole point of Darry going down the pipe near the beginning was because he couldn't see the bottom of the pipe. However, Trish can make out his shock when he notices the body. Darry's flashlight is not providing the light in this scene as the light is coming from the tunnel.