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.
Continuity mistake: During Season 2, Episode 9 (Special Education), just as Blaine is singing "Hey soul sister, I don't wanna miss." for the last time, he is several feet in front of the other Warblers. But during the next shot, as he is singing ".a single thing you do.", he's right in front of them. So he jumped back several feet between two shots.
Continuity mistake: Bob Fossil records Howard saying "Gorilla" on his talk box, which Howard does with a downward inflection at the end of the word. However, every time Fossil plays back Howard's "Gorilla", it has an upwards inflection at the end of the word.
Continuity mistake: During "Brand New Day", at one point, Dr. Horrible stabs a picture of Captain Hammer attached to a dartboard with a handful of darts, all right in the center of the picture. A few shots later as Dr. Horrible sits, suddenly the darts are far-more spread out. (It's in the background and can be hard to see, but it's noticeable.)
Continuity mistake: After the Squirmese chef sets up his additional ingredients, Corky answers the video phone. During Corky's conversation, Al's kitchen can be seen with no trace of the chef or his ingredients.
Continuity mistake: When the Warners emerge from a sealed crate on Miss Flamiel's desk and start singing, Yakko instantly appears behind Wakko and Dot as soon as the shot changes.
Continuity mistake: When Vinnie Jones takes the King to his room, his earring keeps changing from ear to ear between shots.
Continuity mistake: At the diner when Tsunoda and Retsuko are talking, Tsunoda pulls out a red phone with a white heart on it from her purse. In the close up she is pulling it out with her left hand and the phone is horizontal with the heart on its side. It then cuts to a wide angle and suddenly she's holding the phone upright with both hands.