Bag of Money / Principal Simmons - S5-E4
Continuity mistake: Iggy removes his sunglasses - twice.
Suggested correction: The first time he is holding his glasses there was time for him to remove them we just did not see it. The second time we see him remove them.
Parents Day - S5-E6
Continuity mistake: In the scene where Arnold's parents leave for the last time, Grandma's hair is dark at first, then it becomes purplish-gray.
Parents Day - S5-E6
Continuity mistake: In the tricycle section of the last event, the chinpiece of Helga's helmet keeps switching colors.
Helga's Locket / Sid and Germs - S5-E7
Continuity mistake: When Sid decides to be a slob again, he picks up his frog and you can see that he has gloves on. When the following shot shows a close-up of the frog in Sid's hand, the hand holding the frog does not have gloves on.
Beaned / Old Iron Man - S5-E11
Continuity mistake: When Arnold reads to Helga, the book title says "GEO-" and "GRAPHY" (two words); the next day, it says "GEOGRAPHY" (one word).
Ghost Bride/Gearold VS Jameo - S5-E25
Continuity mistake: In the scene where they are running from the second ghost bride, they go into a crypt and close the doors. One of the kids puts a shovel through the handles to keep it shut. In the next shot, it's gone. In the shot after that it's back.