Visible crew/equipment: When Toxie walks into the video store and discovers that a gang is destroying it he grabs one of the gang members and punches him in the stomach. If you look at the guy's belly just before Toxie punches him you'll be able to see a big red spot on his shirt. This big red spot is actually the blood pack that the guy is wearing underneath his shirt and also where Toxie is supposed to hit him.
Continuity mistake: After Claire returns with the contract she gives it to Melvin who asks about the escape clause. The escape clause states that the contract will be null and void only through an act of God and the devil says that God is on vacation. Melvin starts to shake. He's holding the contract in his left hand but in the next shot, a close-up, the contract is gone. The contract then returns to his left hand in the following shot.
Continuity mistake: After Toxie has punched the first guy in the video store, he presses his hand against the wound. When he does this the guy's suspenders are down, but in the next shot the guy's suspenders are back up.
Continuity mistake: After Toxie takes the letter from Apocalypse Inc. from Claire he opens it and reads it. He never puts it back into the envelope, but in the next shot it's magically back in the envelope.
Factual error: As Toxie is removing the guy's intestines with his bare hands, you'll notice that there's absolutely no blood on the intestines.
Plot hole: If the Devil made Claire blind again, how did she read the fine print of the devils contract with Toxie saying that there was an escape pod?
Revealing mistake: When little Melvin gets turned back into Toxie, Toxie charges towards the devil and picks him up, and starts swinging him up in the air. While he's doing that, you can tell the devil has been replaced by a very unconvincing dummy.
Continuity mistake: When the Devil is turning Toxie back into Melvin, watch as he's melting - his jaw is about to come off. Then the next shot shows his skull hit the ground, only his jaw is firmly and secure back in place.
Continuity mistake: Just before Toxie punches the first guy in the video store you'll notice that the guy has a giant pin, about three feet long, tied to his jacket but after Toxie punches him the pin has disappeared.
Revealing mistake: When the school bus is put on top of the cliff by the devil, you can tell they didn't get the bus to go up the hill. They actually dropped it of the cliff, then reversed the film and ran it backwards so it looked like it went up. You can tell by one of the small trees which is flat, but then it stands upright.
Continuity mistake: After the chairman has revealed that he is in fact the devil, he starts to spit slime. His face and goatee are covered in it, but in the next shot when he introduces the five levels of doom, his face and goatee are dry and free of slime.