Continuity mistake: When Mike and Jodi are walking through the "deserted" town, supposedly everyone in town has been killed by The Tall Man, when the Tall Man walks down the middle of the street you can see an old lady pushing an empty shopping cart, and a car driving around a corner in the distance.
Continuity mistake: Jennifer's custom Maverick has nice new tires & hubcaps, but after the car flips they are replaced by cheaper, plain ones.
Continuity mistake: When Michael meets Morningside, as he backs away, he backs into an old lady sitting in a chair. Morningside touches her hand, then walks behind the chair and gestures with his right hand towards Michael, yet when the camera goes back to the old lady, she's still holding his right hand.
Continuity mistake: When Reggie says "Jody died in a car wreck", Jody's car landed upside down in Phantasm and Phantasm II. It explodes right side up in Phantasm IV.