(at around 9 mins) Jason gets his clothing for this installment from the clothesline in the opening scene. However, when Chris has a flashback involving him (at around 50 mins), he's wearing this newly obtained outfit.
(at around 9 mins) The newsreader describes Jason as an ax murderer, which is inaccurate, as he did not not kill anyone with an ax in the previous film. He attacked Ginny with a pick ax rather than an ax, and, in general, his victims were killed using a machete or knife.
(at around 1h 5 mins) Jason stabs Debbie with a knife so long it goes through her and extends a few inches. (at around 1h 17 mins) Chris pulls it from her and stabs Jason with it, yet it is shorter. It is even shorter when Jason throws it at her.
(at around 5 mins) After Ginny and her boyfriend leave the Jason's shack in the opening there is an insert shot of Jason setting the machete on the ground. However, when Jason jumps through the window at the end of Friday the 13th Part 2 the machete is still embedded in his shoulder.
(at around 8 mins) In the TV report in the beginning, the newscaster says there were 8 victims of the previous attack. There were actually 9 victims not including Alice in the beginning of the second movie. Victims in order: Crazy Ralph, Policeman, Scott, Terry, Mark, Jeff, Sandra, Vickie, and Paul. Paul is not seen killed in the second film but Ginny is focused on as the only survivor in the TV report.
(at around 9 mins) In the newscast at the beginning of the film, we are told "Ginny Fields miraculously survived repeated attacks by the ax-wielding killer." In Friday the 13th Part 2, Jason did not use an ax in any of the death scenes. Jason doesn't kill anyone with an ax until Friday the 13th: The Final Chapter.
(at around 1h 11 mins) Chris puts her lantern down on a table in the sitting room, before going upstairs and finding the flooded bathroom. Later when Rick's body is thrown through the window, the lantern has vanished.
(at around 56 mins) When Shelly grabs Vera's ankle, she shakes her shoe off in the over-the-shoulder POV, and it's only held on by the strap around her ankle. In the front shot, it's back on her foot again.
(at around 33 mins) After Ali smashes the windshield, you can see the Olympia beer truck behind him is parked parallel with the road. But when Shelly turns the car around and drives back at him, the truck is now diagonal to the road.
(at around 1h 17 mins) When Chris comes out from the green door waving a knife at Jason, the green door closes all the way behind her. It cuts to Jason and then back to Chris, and behind her in the background the green door is now wide open.
(at around 20 mins) When the kids stop for the police cars who rush by, we get to look out the back window of the car. You can see a car and a road sign there. These two weren't there when they pulled over.
(at around 5 mins) In the recap of Friday the 13th Part 2, Ginny removes Jason's head cloth and leaves it by his head. In the newly filmed shot of him moving the machete, the cloth is suddenly by his chest.
(at around 1h 17 mins) When Chris runs into the bedroom away from Jason, there is a long decorative picture hanging to the left of the window, and between shots a long piece of brown string, hanging down the painting, alternatively appears/disappears.
In the barn towards the end of the movie, Chris is being chased by Jason and the main pathway in the barn is clear of obstacles. However, in the closing shot showing Jason lying with the ax in his head, there is all sorts of clutter behind him with no explanation of how it was placed there.
When Chris and friends stop at Vera's house to pick her up, she comes outside with no suitcases or bags, yet she is able to change her clothes throughout the movie.How can this be if she took no luggage to the lake with her.
Chilli pours popcorn into a sieve and opens the salt and sets it on the table, she then hands a flashlight to Chuck and tells him to go check the fusebox. In the very next shot you see her opening the salt again.
(at around 20 mins) When they pull over to the roadside for the police cars, the van clearly comes to a stop. But when the camera cuts straight to inside the van, the view out of the back window shows the van is still moving.
(at around 33 mins) After Vera says "uh-oh," as she and Shelly sit in the car outside the grocery store, the camera pans around to the side window. You can see a hooded cameraman reflected in the small triangular window, as the camera pans.
(at around 1h 25 mins) After Chris puts the noose around Jason's neck and throws him from the loft of the barn to hang him, she goes down to the ground floor to leave the barn, but the door is secured with a piece of 2-by-4 as a cross board. Chris hits upward with a metal object to release the board. Just as she finishes removing the board, you can see movement of a crew member through the barn door cracks.
The wires controlling the snake (at around 13 mins), harpoon (at around 1h), eye (at around 1h 12 mins), and the knife Jason throws at Chris (at around 1h 17 mins) are all visible when they come at you on the screen.
When Debbie is looking through Fangoria magazine the articles do not match the issue. The two articles, Tom Savini: New Master of Magical Makeup and Twenty-five years with Godzilla, are from issue #1 but the cover is from issue #13. Fangoria #1 can be seen on the drawer when Debbie is deciding which one to read.
(at around 33 mins) After Ali breaks the windshield, the shot from the front of the car shows the glass breaks like a regular window indicating it isn't automotive safety glass. Safety glass has been required by law for new and replacement windshields since the 1940s.
When Andy is cut in half by Jason, blood spurts everywhere yet
when his girlfriend gets out of the shower and walks past the spot she doesn't notice (or tread in) the floor covered in blood. Even though Andy's bisected body is hanging over her head she doesn't notice until a few small drops of blood drip down, despite the massive wound.
(at around 25 mins) When Chris is getting her bags out of the van and Shelly surprises her, you can see Rick waiting in the driver's side rear view mirror waiting for Chris to scream, which is his cue to enter the frame.
(at around 40 mins) When Loco looks up to where Fox is for the second time, after he has told her to get down and has grabbed the container of gasoline, she is gone, but we can see a foot (probably Jason's) stepping out of view of the camera in the lower right corner of the upper barn doorway.
On the back cover of the DVD it says "for another group of naive councilors". The cast in the film are not cast as councilors, they are just friends of Chris, who is taking them for a getaway holiday to her parent's retreat in the woods.