Revealing mistake: There's one scene where the Turtles are surrounded by the Foot. Leonardo reaches behind him for his katanas, but he doesn't unsheathe them. If you look at his elbows, you can see gaps in the pads where the actor in the suit hasn't fully fastened the gloves to the rest of the outfit. (01:05:40)
Revealing mistake: When Bill and Ted leave the house with their "bad" selves, Keanu Reeves' double is seen as they move past the camera. (00:21:20)
Other mistake: Michael McShane's name is spelled wrong ("Micheal") in the opening credits.
Continuity mistake: After finding his son hit a home run in the game with the pirates, Peter decides he must learn how to fly. The ball his son hit comes flying from the sky and hits Peter in the head, knocking him over. When he hits the ground, he is lying on grass, but one second later he opens his eyes on grey rock. (01:28:10)
Revealing mistake: When Angelo is shot in the back at the airport, you can see a pack underneath his shirt when he is rolled over by Utah. (01:39:44)