Continuity mistake: Towards the end when Glen cut his father's arm off, you see him lying there screaming and bleeding. The blood from his arm on the floor is making a puddle and then it cuts to Glen's face. When it shows Chucky's arm (or stump) again, there is no puddle, just blood following the crack in the floor tile.
Revealing mistake: Near the end, when Glenda says, "That's my name. Don't you wear it out," she bends her left hand back and you can see the joint mechanisms (sticking out from under her wrist) that are used to move her hands. This is odd because Glenda is supposed to be a plastic doll in the film, while Chucky and Tiffany are supposed to be animatronic figures brought to life.
Visible crew/equipment: When Jennifer Tilly is being hassled by the paparazzi, she gets in the front of the car, then the camera follows Chucky, Tiffany and Glen's feet hopping in the car. Watch the silver limo bar, the camera dolly track is visible in it. It can't be the limo's feet reflection, because the camera reflection moves and stops the exact same time as the camera stops in its tracks.
Revealing mistake: When Joan is burned and she flies over the railing, you see it's not Joan but a stunt double. The stunt double is also obvious in other shots in the film.
Continuity mistake: When Joan walks in to see Tilly and Stan tied up on the bed, both Tilly's and Stan's feet are tied to the bedrail but are lying flat on the mattress. When Joan is set on fire, there is a shot where you can see Tilly's and Stan's feet again, only this time, they are elevated and resting on the bedrail they are tied to.