Deliberate mistake: Lily was an infant for all of season 5, but beginning with this season, she is around 5 years old. The show didn't jump forward in time, because JT states in a season 5 episode that he is 19, and in the episode this season where he and Rich go to Mexico, he states that he is almost 20, as well as Al and Mark are both still in high school.
Revealing mistake: In the episode where Denise tries on her wedding dress Jim leaves the room to go and wash up. As he opens the door to leave the living room if you look down towards the front door you can see Dave stood by the door frame waiting for the next scene.
Continuity mistake: When Kelly is putting the number card on Logan, you can see one on Kendall behind him, when he shouldn't have had one yet.
My Sister, the Homemaker - S5-E12
Visible crew/equipment: At the beginning of the episode, Jeannie is talking on the phone by the stairs and her sister is hiding behind the banister. Her sister stands up for a moment and shows her full face, revealing that it is actually Barbara Eden's stand-in wearing the green costume.
Revealing mistake: S9 E1 "Bully for Ben": When Ben hits the punch bag sideways, it's easy to tell that someone is controlling the punch bag as it never slows down.
Other mistake: Michael is 40 in Season 2 ep. 20 (Papa Said Knock You Out) while Jr. is 16 in ep. 19, which could not be possible since he had him when he was 16/17ish himself.
Father Frank, Full of Grace - S1-E12
Continuity mistake: When Steve gives Fiona the ticket to Miami he says it is out of O'Hare. When he goes to the airport he is at Midway.
The Spanish Inquisition - S2-E2
Revealing mistake: At the very end when The Spanish Inquisition bursts into the courtroom, you can see that Biggles is not played by Terry Jones (as he is playing the accused judge in the court sketch).
Continuity mistake: In the introduction, when TJ pulls the ball off Gus, Gus is covered in gum. When they are walking into the school, the gum has disappeared.
Continuity mistake: Farzad JinJi is introduced as Dominque in the first season, but he appeared as a different character in the second episode.
Archer Vice: Southbound and Down - S5-E5
Factual error: When the bikers are chasing the bus, one of them crashes into the "Now Leaving Texarkana" sign. However, shortly before this, we see Cyril crashing into the sign reading "Austin. 105 miles." Texarkana is almost 350 miles from Austin.
Revealing mistake: When Brad wears the sunglasses and holds the pole, you can easily see the string that holding it up.
The Burning - S9-E16
Continuity mistake: At the beginning of the episode, when Puddy is farewelling Elaine on the street, he is standing on the sidewalk and leaning through the driver's window. The following shot when she pulls out quickly, you can see through the windows of the car that Puddy is nowhere to be seen.
Gourmet Night (a.k.a. Gourmet's Paradise) - S1-E5
Revealing mistake: When the Colonel first meets Basil, the same shot is used twice of the Colonel twitching.
Continuity mistake: Sue says that she "matured" aka got her period, on Sept 21, but in the episode "Forced Family Fun", when they go camping and she gets it, they go before school starts, which is well before the end of September.
Visible crew/equipment: When Alan views the kitchen, a boom mic shadow can be seen in the top left of the screen. (00:13:05)
The Long Legs of the Law - S2-E1
Revealing mistake: At the very beginning of the episode, Leonard Pearce is waiting for the cue for his character to start looking for his teeth. He's standing in the living room, between his room and Del and Rodney's room. (00:00:25)
Other mistake: Episodes 4 and 5 of season 1 aired noticeably out of order. In episode 4, "The Nanny," Alex's former Nanny, Rosalba, comes to work at his podcast company, and its name, "Ajana," is mentioned a few times. But episode 5, "The Mother-in-Law," starts with the company unnamed; over the course of the episode, Alex learns of the concept of "ajana," the unknown, from his mother-in-law and chooses it as his company's name.
Shrink It Up - S2-E1
Continuity mistake: When Rocky is saying things that she has been pushed into doing, she mentions the time they danced on the wings of a plane. However they didn't do that until a few episodes later.