Revealing mistake: A lot of times in the movie, when the turtles' mouths are wide open, you can see the cast. An example of this is the scene when Raphael wakes up in the bath tub and Leo hugs him. When Donatello tilts his head back and laughs you can see eyes, a nose, and a mouth within the mouth of the costume.Jason Voorhees
Visible crew/equipment: Just before the ceiling collapses on the antique store a boom operator can be seen on the right hand side of the screen.
Continuity mistake: After Raphael has a fit and walks out of April's apartment, he goes up on the roof to vent his anger for a while. Pretty soon, Casey spots him from another rooftop several buildings away while tuning a radio. As Casey looks out at Raphael's faint image in the distance, pay close attention to the background as well as the white building Raphael is standing on (you can notice the Empire State Building among other landmarks). When Casey grabs some binoculars to take a better look, Raphael can be seen resting on a brick ledge. In the following shot Raphael looks out at the city towards Casey's vantage point, but from Raphael's position, the Empire State Building - as well as the white building where he was venting just moments before - are visible on the skyline. Somehow Raphael has managed to relocate to another building's rooftop between shots. (00:38:15)ryguy_1983
Continuity mistake: When Splinter flips Shredder over the edge of the building, Shredder pulls a knife and throws it. When Splinter catches the knife, he catches it with his right hand; in the next shot, Splinter's right hand releases the nunchaku and Shredder falls. The shots are out of order.
Visible crew/equipment: When Michelangelo retracts his head from a sword blow into his shell, you can see a crewman's hands under his armpits, holding and moving his upper arms.
Continuity mistake: In the alphabet game of insults, Donatello calls Casey Jones "elf lips." Casey puts the monkey wrench on the radiator next to the dirty rag, but in the next shot the tool is gone from there and is in his left hand instead, so he retrieves only the rag from under the hood. (00:53:10)Sammo
Continuity mistake: Casey Jones arrives to the save the day. Michelangelo does a Wayne Gretzky reference. Notice in the background Master Tatsu, solitary and surrounded just by old abat-jours and other dusty curio. When he orders in his spartan English to "attack", he suddenly has a bunch of goons all over him. (00:46:05)Sammo