Continuity mistake: During the bank scene, the Joker shoots the bus driver and he falls dead in front of the bus. As the Joker approaches the Bank manager to put the gas can in his mouth, you can still see the body. But after he removes his mask and walks toward the bus, the driver's body is gone.
Continuity mistake: The Joker fires a rocket-propelled grenade at the Tumbler, sending it crashing end over end. In the final tumble, as it loses the last of its momentum, it's rolling to rest on its roof. The camera angle then changes and it's suddenly regained momentum, rolling again so it lands on its wheels.
Continuity mistake: Joker and Two-face are in the hospital; Harvey is about to flip the coin to decide if the Joker lives or dies. The camera angle switches back and forth between the Joker and Harvey. From one angle Harvey is wearing the monitor clamp on his middle finger with the grey wire, from the other angle it is gone. It disappears and re-appears every time the camera angle changes.
Continuity mistake: During the opening bank robbery scene, the Joker reaches down to toss a duffel bag of money to the school bus driver. He is holding his pistol in his left hand and reaches for the bag with his right. But in the very next shot, his pistol is in his right hand and the bag is in his left.
Revealing mistake: As Harvey Dent is tied up in the warehouse with the explosive barrels talking to Rachel, if you look in the lower right hand corner of the screen, a green blanket on the floor moves up slightly as Harvey tries to get out of his restraints. It's too far away for Harvey to touch. A person's fingers or hand is also momentarily visible in the previous establishing shot when Dent is regaining consciousness.
Continuity mistake: When Eric Roberts gets in the car with Two-Face, the car seems to go from being parked to going full-speed in a split-second. As he's getting in the car, Roberts is talking to his driver, and just as he sits down, he sees Two-Face, and the background appears to be moving by very quickly behind him. The car wouldn't have had time to even pull away from the curb yet.
Audio problem: In the opening heist sequence a clown grabs a bald bank teller and the teller says "Please no, no!" while being thrown over the counter, however, his voice doesn't match his facial expression. His voice is loud and terrified in fear and yet his lips and face expression barely react.