Continuity mistake: When Bucky jumps on the hood of the bus to get back in, the Creeper flies from in front of the moon towards the bus causing all the kids to run away. Bucky can still be seen staying put on the hood when they run - however in the next shot of all the kids running you see him at the front of the pack which would have not been possible given that he didn't run right away.
Visible crew/equipment: When the farmer fires the hole puncher cannon at the Creeper the first time with the line attached, the screen changes to a higher view, from here you can see there are two lines attached to the cannon, but he only fired one. This would be for the crew to pull the truck around safely.
Continuity mistake: Just after the man says 'he looks dead to me' (he means the Creeper) he walks past the girl who holds the black guy sitting/laying on the ground. The black guy is buried deep in her arms and he holds his right arm half over his face and on her left elbow. His fellow 'pupils' walk to him. Next shot: his fellow pupils walk to him, but now his right arm is lower, exposing his face and his right hand is now at his chin instead of on her left elbow.
Continuity mistake: When Izzy finds the javelins on the bus, Bucky is the only person at the front of the bus (because he is trying to call on the radio). In the next shot Scotty appears out of nowhere at the front of the bus and yells, "Sticks. You want to hang around here so that you can poke at this thing with STICKS?" with Bucky standing right next to him.
Continuity mistake: After Taggart shoots the creeper the first time, he says, "He's gonna rip my gun out of my truck!". After they jump out of the truck, it gets nearly totaled and the gun is ripped off. Later at the end, he shoots the creeper with the same truck and the same gun, as if he fixed his truck and re-welded the gun to his truck in seconds.
Revealing mistake: When the Creeper has been harpooned, he flies in the air dragging the pick-up truck with him. The pick-up truck moves towards the back of the school bus. If you look carefully you can see that the cable attached between harpooned Creeper and pick-up truck at times hangs too loose to be able to pull the truck, so obviously the truck is moving on its own (with hidden mechanics, which you by the way can't see).
Other mistake: When Coach Hanna catches the cheerleaders smoking, they turn around, caught off-guard, and have to hold in smoke in their mouths. After he turns away to get people back in the bus, they all blow out smoke and cough, even though they hadn't even inhaled any when they turned around.
Continuity mistake: When Rhonda grabs a javelin and spears the Creeper through the head to save Bucky, he loosens his grip and they all back away. The javelin is left sticking out of the hole, jerking around for a bit, and then is suddenly lifted out of the roof. In the next shot of the Creeper on top of the bus the javelin is still in the hole, and then he lifts it out slowly.
Continuity mistake: The first time Bucky is grabbed by the Creeper, Double D and Big K are the first two to run to help him but when the angle changes Double D and Izzy are the first two to reach him. There's no way he'd be able to overtake Big K in the two seconds it takes to run up a bus.