Revealing mistake: When Han shoots at Bruce Willis and the others with the Gatling gun, we see cartridges on the ground. You can tell that they are all blanks. The tip is jagged and has been closed - live ammo just has an open hole where the bullet was.
Continuity mistake: When the WABAC machine is going through the time vortex, trying to escape from the black hole, some tiles get sucked off the WABAC, but in the next shot they are back on.
Other mistake: Near the start of the movie Jon indicates that he has titanium in his right arm, but towards the end of the movie the bullet ricochets off his left arm. (00:08:55 - 01:34:45)
Continuity mistake: After defeating Fulton Balcus, Sean removes the armor and has no clothes on. As Sean and Mizky leave, Sean is wearing sneakers. Mizky only brought him a shirt to wear.
Continuity mistake: During the scenes at her Mother's house, Kate's hair goes from blonde to REALLY blonde.
Continuity mistake: In the scene where John is peeing off Stifler's balcony, he knocks over a plant and knocks out Christy. In the next shot the plant is back, and in the one after that it is gone again. (00:17:15)
Revealing mistake: Gracie hugs the Russian waitress in order to have a better view of the disc hand-off appear on the monitor. As she raises her left hand that holds the book/camera lens, we see that the digital feed that appears on the monitor stays steady and level, even though she is raising the book/camera lens higher and closer to her face. Obviously the feed that we see on the monitor is not taken from the book/camera lens. (00:04:10)
Continuity mistake: The chutes that Wednesday and Pugsley use changes positions when Fester chases Wednesday.
Other mistake: Even though it is snowing throughout much of the movie, none of the snow seems to stick to any of the characters' fur. Even during the fight scene when they are rolling around in it, they are never covered with white.
Visible crew/equipment: When a gremlin attacks the Mum from a Christmas tree, and the tree falls on top of her, you can clearly see a member of the crew with eyeglasses, wearing a red shirt, standing behind the tree pushing it forward on top of her. (00:54:30)
Factual error: When the barracks are completely flooded, Eggsy uses his bare fist to punch through a large two-way mirror to escape. The fact is that any glass (or plexiglas) thick enough to contain hundreds (or thousands) of tons of water without bursting would be as impenetrable as concrete to Eggsy's bare fist. He would need a chisel-tipped jackhammer to penetrate such a mirror.
Plot hole: There are six metal bars mounted around the circumference of the water wheel's axle. In the wheel's interior, when Jack frees himself he lands on his feet, begins to run and promptly hits his head on one of those mounted axle bars, then falls out. Moments later, when Jack returns and runs in the wheel, he is shorter (way more than a foot) than all six of the mounted axle bars spinning with the water wheel, which would make that previous shot impossible, however humorous it is. (01:52:40 - 01:53:55)
Continuity mistake: When Hal's co-workers bring him a cake for his promotion, Rosemary takes a slice out for herself. They change shots a couple times, and the size of the piece missing from the cake changes several times, and the layers of the cake change as well.
Other mistake: The envelope with the letter for Amanda is suddenly in a very good condition as it ends up in the peanut bowl... even though it has been in the trash, had chewing gum attached to it, been trodden on, had a beer barrel rolled over it, etc....
Continuity mistake: At the beginning of the movie, Harry's van has bucket seats, yet later on when the "gas-man" rides along, he is sitting on a bench seat in-between Harry and Lloyd. (00:38:00)
Suggested correction: Mental isn't sitting on a bench seat, it's implied he's sitting on the floor of the van in between the both of them. Although hard to see, the backs of the bucket seats can still be seen behind Harry and Lloyd at certain points. You see a fair bit of it behind Harry whilst he's dancing as Lloyd sings the line "and if that mocking bird don't sing".
Character mistake: When Stuart calls home from the pay phone he's talking into the wrong end of the phone.
Visible crew/equipment: In one scene Ace is drumming large mushrooms supposedly growing on the side of a tree. When Ace knocks only one off (the very last mushroom, he hits it off the tree completely and you see) a metal spike that held all the mushroom props in place visible on the tree.
Continuity mistake: In the convenience store, Link weezes the juice and gets slurpee all over his shirt. He gets kicked out and leaves, but 2 seconds later he comes back in the door and says, "I'll be back". At that point he has nothing on his shirt at all and it's completely dry.
Plot hole: Prior to the final show, when the horsemen are performing separately at different locations in London. [Scene X] Jack is busy with his card swap trick. While others are doing their tricks too, [Scene Y] McKinney is believed to be tricked once again by his face sharing brother at another location... Dylan gets a call and then he calls everyone to wrap up and meet somewhere. [Scene Z] Jack also wraps up and leaves the place... OK. Later after the expose in final show McKinney tells the story about how Jack successfully hypnotized his brother [in the Scene Y]. How could Jack be at two different locations at the same time? He was performing somewhere else when he did hypnotism at another location and then wraps up his trick back where he started.
Continuity mistake: There is a scene where everyone is dancing. It's towards the end but not at the very end. One of the employees of the record store takes his shirt off. Then the camera cuts back and you see the entire group of people dancing. If you look at him he has his shirt back on. Then a couple of shots later he has it back off again.