Revealing mistake: When Nica crawls to the elevator to escape Chucky, she bends her legs in order to shut the elevator door. She is meant to be a paraplegic and have no feeling in her legs.
Revealing mistake: When Nica goes to investigate the screams in the first part of the movie, as she opens and closes the door she appears to be moving in a way that implies she is standing and not sitting in her wheelchair, this completely contradicts her being a paraplegic.
Revealing mistake: When the pastor is beheaded you can see a clear tube inside his neck that is squirting blood.
Suggested correction: That's actually supposed to be the top of his spinal cord. The blood is noticeably coming from behind it if you look closely.
Continuity mistake: Barb's eyes are green throughout the movie, but when Chucky stabs her in the eye, the eyeball that rolls down the steps is blue.
Revealing mistake: When we see Jill's webcam image on the remote laptop during the electrocution scene it is from Chucky's point of view, and not her laptop's webcam.
Revealing mistake: When Chucky is trying to kill Nica with the fumes of the car, you can hear him hit the gas and the engine revs, but the smoke from the silencer has a constant flow.
Plot hole: When Chucky is decapitated, no blood comes out. He still has the scars from Bride/Seed of Chucky so that means he's still in the same doll's body. The longer he remains inside the doll the more human he becomes, so he should definitely bleed by this point in time.
Suggested correction: There's no telling exactly how his Voodoo works.
Factual error: Chucky is not tall enough to rev the engine of the car in the garage when trying to suffocate Nica.
Suggested correction: I watched the scene and it's clear Chucky wasn't using a brick on the accelerator to rev the engine. However, Nica is paralyzed and there are devices you can install on a car that allows a paralyzed person to operate the gas and brake from the steering wheel, so Chucky could rev the engine without touching the gas pedal.
Suggested correction: All he would have to do is stand on the gas pedal.
He's standing at the wheel the entire scene. He's not tall enough to be doing that and pressing the gas pedal.
He could have used a brick or something to keep the gas pedal down and then climbed up to the wheel.
Except if you watch the scene, the engine revs up and down, not something putting a brick on the gas pedal would do.
Continuity mistake: When Barb first enters the house, Father Frank walks up beside her. The shot cuts. Barb steps onto the spot of blood, and the camera pans up. Father Frank walks up beside her a second time.
Continuity mistake: When Nica finds Ian asleep next to Chucky and shuts off the projector, she puts her right hand against her chin. It then cuts to an over-the-shoulder shot of Ian. When it cuts back to Nica, her left hand is against her chin. (You can tell in the over-the-shoulder shot that she didn't move at all, and thus didn't switch hands.)
Continuity mistake: When the cop calls Tiffany, his mouth goes from closed to open between cuts.
Continuity mistake: When Nica is wheeled out of the courtroom, when it cuts to the wideshot, suddenly she has moved back about 10 feet between cuts and is wheeled through the same area a second time.
Continuity mistake: When Nica stabs Chucky, how deep the knife is in his back changes between shots.
Other mistake: When Nica is dragging herself away from Chucky, you can see her calf muscles flexing and see her lift her legs above the floor for a second, even though her legs are supposed to be paralyzed.
Other mistake: When Chucky is telling Nica the story, his reflection in his knife is not mirrored, as it should be.
Continuity mistake: When we see Sarah's death, Chucky in the background has the "stitched" face. However, this makes no sense as when this happened, he would have had the regular doll face still.
Continuity mistake: In the flashback, when Charles pulls the knife out, Sarah goes from having her mouth open to having her teeth gritted instantly between cuts.
Continuity mistake: After the wheelchair smashes on the ground, its pieces and the banister pieces change positions next time we see them.
Visible crew/equipment: When Nica is pushed through the railing by Chucky, you get a quick but clear look at the stunt double's face, who looks nothing like actress Fiona Dourif. Her arms noticeably also get more toned when this happens. Finally, for a second, you can see her moving her one leg, which shouldn't happen since Nica is supposed to be paralyzed.
Revealing mistake: When Ian's jaw gets hacked off, the blood that splatters on his shirt almost all just beads and rolls off, rather than sticking, and is super thick, revealing it's fake.