Continuity mistake: When Stewie is building with blocks, you first see a pyramid with three blocks on the bottom and two on the top. The shot changes, and he puts two more on the top, near the edge. When the shot changes again, suddenly there are five blocks on the bottom, six on the second layer, and two on the top near the middle. The letters and pictures are also all different.
Factual error: When Peter has his KISS trivia game with Dave the nudist, he asks what the ad read that brought Peter Criss to KISS, and they both answer in unison: "Drummer willing to do anything to make it". In fact, the ad read: "Drummer with 15 years' experience willing to do anything to make it". As the original ad is referenced and shown in several biographies on KISS, as well as the "KISS: eXposed" video, it's not something these two trivia experts would have missed.
Factual error: When Brian fires his pistol in the air, eventually killing the Super Devil, we hear six gunshots, each followed the distinct clink of the ejected cartridge hitting the ground. Trouble is, Brian is firing a revolver, which does not eject the cartridge after the bullet is fired. Only automatics do that.
Continuity mistake: As Stewie is about to eat his brisket (just before he throws it at Meg) he is cutting part of it off. Just as he cuts through the shot cuts and you can see the brisket is now back in one whole piece. You can also see the mashed potatoes change from white to green.