When Kumar is chasing after the antagonist towards the end of the movie, one shot shows him on an open road. However after he knocks two henchmen drivers out their windows and the cars explode, one shot shows the cars exploding from a parking lot - where ironically Kumar is seen passing from behind the chaos.
When the bad guys fire their bazookas at the protagonist during the car chase, two missiles are shot out. Yet when the missiles hit two cars, the windshields crack in two different spots - making it appear there was more than one.
At one point in the car chase, a white and red car crash into each other and Kumar jumps over them; a missile is fired (from one of the trucks) at the two cars and they explode. However in subsequent shots, the trucks - that are supposed to be riding next to the antagonist - have vanished.
Kumar launches himself into the air from a ramp using his rollerblades; one shot he's holding the rope, another shot he's not and in the third shot, he's gripping it as he sticks the landing onto the antagonist's car.
The antagonist falls off a hot air balloon fighting Kumar and lands hundred of feet below a lake; there would have been a very high risk of injury or even death in this case. Falling into water from 50 or 100 feet, or above, is like hitting concrete as the water cannot move away fast enough to let your fall be cushioned, as it is when you dive into a pool from a five-foot or ten-foot diving board.
After Kumar knocks two cars over, they slide into several vans and explode; yet the rest of the explosion is able to spread to several parked vehicles in the distance thus causing them to explode and catapult into the air.
After a car comes crashing down adjacent to one of the trucks with Kumar managing to dodge it, the rope that Kumar holds onto in one shot is clearly floating in the air and not clinging to the car like it's supposed to - in most of the shots of the chase.