Continuity mistake: When Lily's mother is looking at the gift Lily has just opened, the blue bow on the gift vanishes and then reappears between shots.
Dowisetrepla - S3-E7
Character mistake: In the scene where Robin and Lily are talking in the kitchen, Robin makes a reference to Mount Waddington being the tallest mountain in Canada. The tallest mountain in Canada is actually Mount Logan.
How I Met Everyone Else - S3-E5
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.
Nothing Good Happens After 2 A.M. - S1-E18
Continuity mistake: In the bar when discussing Ted going over to see Robin, the beer bottles in front of Marshall keep moving with no-one touching them. (00:07:50)
Intervention - S4-E4
Revealing mistake: In the flashback when Ted damages the ceiling beam with the flail, you can see that the damage is already there before Ted actually hits it.
Audio problem: When the woman catches Barney doing The Naked Man, she yells at him to get out. After Barney says "Just have to grab my suit, it's very expensive", she says "Get out!" twice. When she says it the second time, she quickly turns her head and her mouth doesn't seem to move with the audio. (00:19:10)
Continuity mistake: When Ted is giving up with Marshall's best man speech he is holding a pen in his hand as well as a beer bottle. In the next shot the pen disappears and he is just holding a beer bottle. In the next shot the beer is on the coffee table and Ted drops the pen onto the coffee table.
Monday Night Football - S2-E14
Continuity mistake: When the gang are about to watch the Super Bowl, Marshall is holding a chicken wing which vanishes from his hand when the camera angle changes.
Monday Night Football - S2-E14
Continuity mistake: In the classroom, Marshall squirts juice on to the boy's clothes then puts the juice pouch flat on the table. In the next shot, the pouch is standing upright.
How Lily Stole Christmas - S2-E11
Continuity mistake: When Ted, Robin and Barney are having a meal at the bar, we see Robin lift her drink to her mouth, then the shot changes to another angle and we see her lift the drink again.
Continuity mistake: At the courthouse, we see Marshall, Lily and Barney walk around the corner towards the bench twice, from two different angles.
Continuity mistake: When the gang are drinking a toast to Ted at the end of the episode, Robin's glass of champagne moves from her left to her right hand instantly when the camera angle changes.
Continuity mistake: When Robin and Ted are at the bar planning their weekend away together, the level of beer in the glass next to them goes up and down between shots. (00:10:00)
Life Among the Gorillas - S1-E17
Continuity mistake: When Lily and Marshall are talking at the apartment, just after Marshall gets off the phone to his friend from work, Lily's necklace changes position between shots. Sometimes it hangs straight down and sometimes it is to one side.
The Wedding - S1-E12
Continuity mistake: In the first scene at the bar, as Ted heads off to speak to Robin, Marshall's beer goes from at his mouth to on the table instantly between shots. (00:02:15)
Continuity mistake: In the previous episode "The Wedding", Ted and Victoria first see each other whilst Ted and Barney are sitting together and both drinking champagne. In this episode, when the same glance is exchanged, a bridesmaid is sitting with Ted and Barney, and Ted is now drinking what appears to be whiskey. (00:01:00)
Chosen answer: She was finally shown at the very end of the last episode of season 8, continuing into season 9. The actor's name is Cristin Milioti: http://www.imdb.com/name/nm2129662/.
Knever