Continuity mistake: In Ted's flashback where Barney's mysterious saboteur is talking to Lily, the girl has straight blonde hair. In episode 14, "The Bracket" where his saboteur was first introduced and she originally spoke to Lily, she had curly blonde hair in the same sequence.
Continuity mistake: When Lily is selling her favourite dress and is saying how she got a two syllable damn, the flashback shows her with the hairstyle she got after coming back from San Francisco, even though she said it happened in 2004. She should have had her shorter, lighter coloured hair.
Continuity mistake: When Lily goes to the bar with her friend Michelle, Barney says "I want her around all the time." It then cuts from Barney to Lily's slightly shocked looking face, obviously from a previous cut/scene change, sitting at the table with them - she should still be walking to the bar with Michelle.
Continuity mistake: During the flashback in which Barney recounts the story of how he and Ted met (which was previously shown in the pilot episode of the series), there is a green circular plaque (that reads "Winner of the Queen Cup") on the wall in the background which wasn't present in the pilot episode. Also, Barney's left arm is in different positions than it was in the pilot.
Continuity mistake: When Ted, Barney and the girls are heading to the South Bronx in the cab, keep watching Colleen's head, near when Barney says, "Somebody's been watching too many Seinfeld reruns", her head moves instantly between shots, from looking towards Ted to looking at Barney.
Continuity mistake: In the scene where Ted goes over to Robin's apartment to yell about their breakup, Robin says "You shaved" and "I liked the beard," implying that this is the first time she has seen Ted since he shaved. But the night before she was in the kitchen at his apartment asking if he was okay with her dating Gael. At that point Ted had already shaved.