Arnold's Room / Helga vs. Big Patty - S3-E4
Continuity mistake: In the locker room, Sid's hair goes from stringy to full and back to stringy.
Curly Snaps / Pre-Teen Scream - S3-E6
Continuity mistake: Pre-Teen Scream: When Phoebe shows up at Helga's house to pick her up for the concert, Phoebe is wearing a red outfit with a red scrunchie in her hair. Thereafter, for the rest of the episode, her red scrunchie changes to her normal yellow one in some shots. (00:15:46)
The Aptitude Test / Oskar Gets a Job - S3-E9
Continuity mistake: Oskar Gets a Job: After Arnold comes home after delivering the newspapers for the second time, he runs up to the door, but in the next shot, he somehow ends up at the window. His helmet also disappears between shots. (00:19:37)
The Aptitude Test / Oskar Gets a Job - S3-E9
Continuity mistake: Oskar Gets a Job: When Arnold and Suzie are in the laundry room, Suzie says that she wishes Oskar would do what he says he's going to do. In the next shot, the washing machine and the dryer switch places. (00:21:10)
The Aptitude Test / Oskar Gets a Job - S3-E9
Continuity mistake: Oskar Gets a Job: When Arnold and Suzie are doing laundry together, as Arnold talks about how Oskar was just fooling them all, he starts walking away from the dryer. In the next shot, he is walking away from the dryer again. (00:21:16)
The Aptitude Test / Oskar Gets a Job - S3-E9
Continuity mistake: Oskar Gets a Job: When Oskar overhears Arnold and Suzie talking in the laundry room, he is standing next to the light coming from the room. As she starts to walk upstairs, he is suddenly walking out of the light area. (00:21:25)
The Aptitude Test / Oskar Gets a Job - S3-E9
Continuity mistake: In "Oscar Gets a Job", Oscar goes around asking people for money. When he talks to Ernie, you can see that there is a phone and a light to the right of the door. When Arnold confronts Oscar in the hall, you can see Ernie's room (7). The phone has disappeared.

Arnold Betrays Iggy / Helga and the Nanny - S3-E10
Continuity mistake: Arnold Betrays Iggy: When Arnold goes to Iggy's home near the start, the front doorknob is on the left side of the door, but the next time Arnold goes to see Iggy to bring him the box of chocolates, the front door opens the opposite way, with its doorknob now on the right side of the door. (00:01:20 - 00:06:40)
Career Day / Hey Harold! - S3-E11
Continuity mistake: There are more than 16 slips in the hat, but only 16 students in class, and only 12 hands went in to pull out slips.
Arnold & Lila / Grand Prix - S3-E13
Continuity mistake: Arnold and Lila: Helga writes "Arnold loves Helga" on the wall, then replaces "Helga" with "Lila". In the next few shots, the way the word "Lila" is written changes four times. (00:02:48 - 00:03:21)
Arnold & Lila / Grand Prix - S3-E13
Continuity mistake: Arnold and Lila: When Lila starts talking to Arnold in the cafeteria, the sandwich on Arnold's tray has sandwich bread, but in the next few shots, they change to hamburger buns. (00:04:06)
Arnold & Lila / Grand Prix - S3-E13
Continuity mistake: Arnold and Lila: When Arnold and Lila sit down at the table, the borders of their trays are missing, then return in the next shot. (00:04:20)
Arnold & Lila / Grand Prix - S3-E13
Continuity mistake: Arnold and Lila: Arnold and Lila have milk cartons on their trays when they sit down at the table, but in the next shot, Arnold's milk disappears, and Lila's milk is beside her tray. (00:04:20)

Arnold & Lila / Grand Prix - S3-E13
Continuity mistake: Arnold and Lila: On the bus, when Arnold tells Lila that he doesn't like her like her, Lila is smiling at him. In the next shot, she is suddenly frowning. (00:07:01)
Arnold & Lila / Grand Prix - S3-E13
Continuity mistake: When Arnold, Sid, Eugene, and Stinky are arguing about the name of the go cart the name is already painted on. (00:17:20)

Arnold's Thanksgiving - S3-E14
Continuity mistake: When Helga is backstage preparing for the play, there is an "H" on the left side of her costume. When Phoebe tells her that she's on, she turns around and the "H" is not on her costume, then reappears a moment later. (00:03:32)
Arnold's Thanksgiving - S3-E14
Continuity mistake: When the play finishes and all the kids are standing on stage, Arnold and Helga are holding hands. Arnold looks at Helga, and Helga pulls her hand away. When the shot changes, they are holding hands again. (00:05:17)
Arnold's Thanksgiving - S3-E14
Continuity mistake: When Arnold's family is sitting around the table on Thanksgiving, there is a blue bowl with a spoon in it where Arnold is sitting. A few shots later, the bowl changes to white, and the spoon is gone. In the next shot, the bowl is blue again, and the spoon is back. In the shot after that, the spoon disappears again. (00:06:34 - 00:07:08)
Arnold's Thanksgiving - S3-E14
Continuity mistake: When Joey is shown in close-up, his missing tooth looks like it's there but it's covered with something black and his missing tooth keeps reappearing and disappearing in the last scenes.
Suggested correction: Joey never appears in this episode.

Helga's Show / The Flood - S3-E15
Continuity mistake: Grandpa's rubber raft got much bigger between the time he left the greenhouse and the time he arrived.