Continuity mistake: There is a scene about 2/3 of the way in the movie where you see Jamal (Martin) standing by the lake and his chain is under his shirt, he looks back into the forest and his chain is hanging out of his shirt, then he goes back to the lake and his chain is under his shirt again. (00:58:30)
Other mistake: When Martin Lawrence falls over the railing in attempt to get the mysterious necklace, the camera goes to another shot that pulls away from the moat. You can see the logo on the back of Lawerence's cover-alls swimming away at the corner of the screen, when he's supposed to be under water. (00:06:15)
Revealing mistake: During the dancing scene, Jamal shows the percussionist how to use the tambourine first, then tells him to start drumming, so he puts the tambourine down. However when he cues in the guitar, the tambourine starts to play again with the drums and guitar. A few shots later, with the tambourine still playing in the background, you can see the percussionist's tambourine sitting on the table next to him where he had left it.
Continuity mistake: When Jamal is trying to ride a horse for the first time, he rides to a stable. When Jamal leaves the stable, he has wheat on his shoulders. He takes it off, but in the next shot he has wheat on his shoulders again. Then in the next shot he does not have wheat on his shoulders anymore. (00:26:40)
Factual error: Towards the end, when the medics are reviving Martin Lawrence, they are using a defibrillator. You can hear the sounds of the defibrillator charging and then discharging. They then show Martin Lawrence wake up, but he is fully dressed. In order for a defibrillator to work, it must come in contact with the skin. I doubt they had enough time to redress him after using it on him. (01:22:40)
Continuity mistake: When Jamal is standing next to the guards when he arrives to the middle ages, small cabins are visible, but when the rebels are attacking, there's a wide shot of the field in front of the castle entrance. No cabins are visible.
Continuity mistake: At the end of the movie when Jamal has been pulled out of the water and taken care of, his clothes go from entirely soaked to completely dry. They CANNOT dry that fast, in that amount of time.
Revealing mistake: In the final battle scene, Jamal is hitting one of the soldiers with his leg. As the soldier falls, it's clear that he throws himself back intentionally.
Plot hole: The legend of the black knight (in this film) is that he can breathe dragon's fire. Jamal somehow rigs up his aerosol spray-can inside his helmet to shoot out the flames. However, there are three problems with this: one, how did it fit in the helmet? Two, how did he activate the spraying mechanism without his hands? And three, how did he even ignite the spray? (00:49:15 - 01:13:55)redbaron2000
Continuity mistake: When the men are sitting at the round table and Jamal is introducing his fast food restaurant idea, the table is empty and then Jamal's paper scroll appears there, then the table is empty again and Jamal opens the scroll on the table. (00:39:25)
Plot hole: When Jamal saves Knolty's life and is invited into his home, he leaves his work jacket at the lake shore. This jacket is where he kept his spray-paint. However, later in the movie Jamal has somehow recovered his spray-pain.