Continuity mistake: When Chucky kills the coroner there is a generous amount of blood splashing on the gravestone. But in the next shot we can see that he is standing next to the gravestone. Chucky shot the coroner in the back of the head since he was looking in the other direction and is falling on his face, so there should be no blood on the gravestone.
Continuity mistake: Jade is in the grave when she throws the amulet to Chucky. Seconds later, after Jesse shows up, it cuts to her standing out of the grave, but she wouldn't have had time to climb out yet.
Continuity mistake: Just after Chucky blows up Needlenose's cop car a bonnet or something flies off. In the next frame someone is in the payphone then a fraction of a second later they are outside it running away about three feet from the payphone as it disintegrates.
Continuity mistake: In the first film, when Charles Lee Ray died and the Police Officer found him, his eyes were open, his mouth closed, his face clean, clothes in perfect condition, and head staring straight up into the sky. When Chucky holds up the picture of him dead in this one, his eyes are shut, his mouth is open (and there's blood coming out of it), his face is dirty and facing to the side, he's missing parts of his clothing (e.g. his tie), and his shirt is now wide open. His body is still in the same place it's was when he died, because the floor is the same, and there's doll boxes around him.
Continuity mistake: When the cop finds the dead Tiffany doll shortly before she is giving birth to the baby doll there is neither blood on her dress nor a hole in it. But in the first shot after she was stabbed she is lying on her back and her dress has blood all over it and a pretty big hole in it.
Continuity mistake: In the beginning when Tiffany is taking a bath and Chucky escapes out of the crib he walks in there and the curtains had 3 butterflies on them. Then the part when Jesse walks in to the trailer you can see that the butterflies are now on the other side of the curtains.
Continuity mistake: Tiffany drops Chucky in a prison-like playpen she calls the "nursery" and closes the cage, causing a folded purple blanket over the hood to slide back, then locks the cage to the hood. In the full-view shots, the blanket is up to the lock, and in the close-up shots of Chucky, the blanket is against the wall.
Continuity mistake: When David opened the chest and saw Warren inside, Warren's shirt was soaked in blood. When he opened it again to show Jesse and Jade, his shirt was completely clean; not a sign of blood anywhere.
Continuity mistake: There is a scene where Jade, Jesse, and the two dolls pull up to a wedding chapel. We see them pass a neon statue of what appears to be the Virgin Mary. While Jade and Jesse are inside the chapel getting married, Tiffany looks out of the windshield and comments on how beautiful the statue is. Apparently Jesse backed the van up about 50 feet before parking it, and the chapel apparently moved with him.
Continuity mistake: When Jade pulls the amulet off Charles Lee Ray's skeleton, she snaps the neck and it falls off. A minute later when Chucky falls into the grave the head is back on.
Continuity mistake: When Jade and Jesse begin making out in the car, Jade is climbing into the backseat with both her hands around Jesse. When it cuts, Jade has her right hand on the driver's seat. (00:08:05)
Continuity mistake: When Tiffany is talking with the gothic guy that has Chucky on his stomach, you can see Chucky's eyes change position. First they look at Tiffany then they look straight forward. (00:16:00)
Continuity mistake: In part 3, the left side of Chucky's face was sliced off, but in this film Tiffany sews the right side together.
Continuity mistake: When Russ is lying down on the honeymoon bed you see him lying on his stomach. When the shot changes he is lying on his side with his legs crossed. (00:53:40)
Continuity mistake: When Bailey has parked and looks at the bag the tag on it change position between the shots. (00:02:20)
Continuity mistake: When David discovers Jade's dead uncle in the van, he grabs the uncle's glock pistol and actually cocks it twice before running out to the truck splatter scene.
Continuity mistake: When we see Tiffany walking away after killing Bailey, she is carrying the bag in her left hand. When it cuts we see her walking with the bag in her right hand and then she switches it over to her left hand again. (00:04:05)
Continuity mistake: When Tiffany files her nail after killing Bailey her hand change position between the shots. (00:03:25)
Continuity mistake: When Warren gets nailed, his face is contorted in a certain way. When the kids are leaving his house, his face is shown again and the contortion is very different. (00:41:15)
Continuity mistake: When Tiffany puts the doll dressed like a bride in the cage with Chucky, she throws a handful of rice in Chucky's face and most of it falls off, but the next time we see Chucky a lot of rice is sticking on his face. (00:27:05)
Answer: There's two possible explanations. First, and the most likely, is that this is simply what's referred to as a "retcon." (Short for "Retroactive Continuity") A term to describe new information/rules/backstory/etc. that are introduced in order to alter the path of a story, or impose new ideas into a narrative. In this case, the series creator and writer Don Mancini needed a reason for the characters to go on a road-trip, hence he created this new idea for an amulet that Chucky need to obtain. And basically, Mancini himself has admitted that he will often change the rules for the series as needed from film to film based on the story he wants to tell, which makes this the more plausible explanation. The second possible explanation is that you could argue that the amulet will allow Chucky to transfer his soul regardless of how long he's been in the doll's body, surpassing the time limit imposed in previous films. But in all seriousness, the former is the more likely explanation. They just needed a new story-element to justify the road-trip aspect of the story.
TedStixon
Both answers work for me. Thank you.