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.
Audio problem: Just after Peter graduates from the Police Academy, he goes home to Lois and draws his gun in the kitchen, which gets Lois very excited. Every time Peter fires his revolver, you'll hear a soft, but distinctive clink briefly after each shot. This clink comes from shell casings hitting the floor, which revolvers make impossible. Revolvers are designed to eject expended shell casings only while its user is reloading, not after each shot is fired. Only semiautomatic firearms immediately eject expended cartridges immediately after having been fired. Unless I'm mistaken, the entire gunshot sound originally came from a 9mm semiautomatic pistol.
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.