Other mistake: When Miyagi throws Mike into the light switches, the lights go out but the switches never change position.
Plot hole: Daniel first needs Miyagi's signature (which Miyagi refuses) to enter the tournament. However the rest of the movie focuses on Daniel's signature needed to enter instead. Didn't Miyagi officially need to sign? How did it suddenly switch?
Factual error: The storyline in Karate Kid 3, based on the happenings and reference points of the first two movies, is supposed to take place roughly about late 1984, or early 1985. However, if you look close at the beginning of the film when Terry Silver drops off John Kreese at the airport, there are several cars that are definitely later 80's models.
Continuity mistake: When Mike Barnes walks into Mr Miyagi's back garden where Daniel is training, they fight and Terry Silver appears. When Terry puts his book to Mike's face, in the first shot it's on the right side of Mike's face, but next shot on his left, then back on his left. (01:03:25)
Continuity mistake: When Daniel is being beaten up by Mike Barnes in the Bonsai store, just after Daniel breaks the glass in the window, look to the left of the screen. There are 4 crates, 1 on top of each other, then when Mike throws Daniel away after punching him, look in the background there are 3 crates and then two next to the 3 crates piled up instead of 4, like we saw in the previous shot. (00:46:30)
Continuity mistake: At the end of the final match, the announcement is made it's the first time in history the defending champion kept his title. Yet in Karate Kid 1 Johnny Lawrence had already won the championship twice and was there for his 3rd time.
Continuity mistake: As Mike falls after hitting the light switches in the dojo, a quick shot of his foot shows he is wearing black shoes when he was barefoot in all the other shots.
Continuity mistake: When Daniel and Jessica are about to climb back up the cliff face, they both tie the ropes to their harnesses with a knot at the end of the rope, yet when you see a shot from the top of the cliff face, you can see quite a lot of rope trailing behind Jessica which shouldn't be there.