Fright Night - S4-E6
Plot hole: After the girls get their revenge on the boys in the attic, they explain the mysterious "I must have air" voice from the trunk as it's revealed to be from a tape recorder. Marcia mentions a set up the girls had where they played the tape recording (from their bedroom) when they were ready. This is impossible as the recorder was in the attic trunk and the play button would have had to be manually pushed down by an actual person to activate.
Character mistake: At the end of the episode when all the kids line up to head upstairs, Mike gives instructions to line up according to their size (big to small). If you notice carefully when the kids all line up, Peter stands behind Marcia, yet he is slightly taller than her.
Continuity mistake: At home, before leaving for the Grand Canyon, the trailer was much taller than the car, and looked more like a motor home. After that, it becomes a different vehicle more like a trailer, about the same height as the car. When the prosecutor steals the car, it's the tall version, and when they arrive at the Grand Canyon to look at the view, there's nothing attached to the car bumper. When they leave the Grand Canyon it's the shorter version, back to being a trailer.
The Dropout - S2-E1
Other mistake: When Greg is in the kitchen getting ready to leave for the baseball game, there is a number 53 on the back of his jersey. In the following scene at the baseball park, there is another man with his back turned throwing practice balls, who also has the number 53 on the back of his jersey. It is clear that it is not the same person.
Lost Locket, Found Locket - S1-E25
Continuity mistake: When they are getting ready for the reenactment of the night when Jan lost her locket, Greg is about to eat an apple when the boys walk into their room. When Greg sits down, his apple is mostly finished.
The Dropout - S2-E1
Character mistake: When Greg was in his room talking to his parents, he said that Joe DiMaggio, Mickey Mantle and Yogi Berra never went to college. Joe DiMaggio attended Yale University, Mickey Mantle attended the University of Oklahoma and Yogi Berra attended Montclair State University.
Suggested correction: DiMaggio dropped out of high school and worked odd jobs before playing semi-pro ball. His son, Joe DiMaggio Jr attended Yale for one year. Mantle was offered a scholarship to Oklahoma to play football, but he never went. He started playing semi-pro ball at the age of 17. Berra dropped out of school after the 8th grade and then signed with the Yankees when he was 18 (but served in the military before playing). Montclair State University gave Berra an honorary degree in 1996.
The Voice of Christmas - S1-E12
Revealing mistake: Carol's hair is quite noticeably shorter in an almost 'Twiggy' bob. When in the prior episode 'Vote for Brady' it was past her shoulders, curled into a very fashionable bubble flip. Not that she wouldn't have visited the stylist after the campaign. Just a very noticeable difference.
Suggested correction: The episodes were aired out of order, so this episode did not immediately follow the previous episode in production. Plus, this was a Christmas episode and Carol was preparing to sing in the holiday service, which is just one possible reason why she'd change her hairstyle.