Other mistake: Early in the film, Jim Carrey is watching TV during a sports segment. He is watching Channel 7, the station he works for. This clip they showed was of actual WKBW sports director John Murphy. The clip they showed was taken directly from a real WKBW newscast, with the authentic news set, and graphics. However, when they show a clip of Ch. 7 News later, there are completely different graphics, and a completely different news set, both made for the movie.
Continuity mistake: After the riot in the streets of Buffalo, Bruce meets up with God again in the Omni Presents building. They discuss how everything is going wrong. At the close-up shot of Bruce's face when he says, "What do I do now?" the frame is flipped. You can tell this because his hair is parted on the wrong side and his nose looks different.
Revealing mistake: In the scene with the accident, the car already has bumper damage just before it hits the pole.
Visible crew/equipment: When Bruce goes back to the building toward the end of the movie looking for God and finds it deserted, as he runs through it, you can see the shadow of a figure (a crew member) on one of the columns on the left. It even slightly moves as he's approaching the ladder as if trying to duck away from behind.
Continuity mistake: When Jim and Jennifer are in the kitchen and Jennifer is commenting on how she thinks her boobs have gotten bigger, Jim is squirting ketchup onto his plate. When he first does this the ketchup goes everywhere all over his plate, cuts to Jennifer and then back to Jim and the ketchup is now in a nice neat pile.