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: When Peter, Quagmire and Cleveland become cops because Joe trains them and they are all at Peter's, Joe has binoculars and is looking across the street and saying he is watching his wife Bonnie in her house. In just about every episode it is stated that Joe and Bonnie's house is right next to Peter's. So why is he looking across the street when their house is next to Peter's?
Other mistake: Peter goes back in time and sees Lois at age 18. Death says everyone will see Peter as being 18 too. Problem: Lois and Peter aren't the same age. In later episodes, Lois reveals she's 2 years older than Peter so Peter should be 16 when he meets Lois.