In the first movie, Jonathan mentions having six siblings. However in the second one he has only three.
The Slurpee machines change flavors when the view is changed to the store security camera.
In several instances throughout the film, Dracula jumps from having long, sharp nails, to short round nails, and then back to long, sharp nails.
In the first film, Mavis asks Dracula to erase her memory, to which he responds "there's too much I want you to remember." This establishes that vampires can use mind control on other vampires, yet when Dracula attempts to hypnotize a camp worker, the worker states that it won't work because he (the worker) is a vampire.
Mavis' teeth become multi colored after drinking multiple Slurpee. They are normal color until she drinks the last one.
After Dracula cracks his phone screen, his image is cracked on Mavis's phone. When a cell phone has a cracked screen, the person on the other end cannot see the cracks.
Dennis dropped from the tower for more than 20 seconds before being caught by his grandfather. In reality, the tower should be over 2,000 meters tall, surpassing all the current tallest buildings in the world; but in the early version of the screenplay, the tower was described as merely 200 feet high.
It's about a 15-16 hour flight from Transylvania to California. The time in Transylvania doesn't change when Mavis and Johnny get to California. By the time their flight arrived it should be 5-6 pm in Transylvania, not 1am as suggested.
If vampires have no reflections, Mavis and Dracula should not be able to video chat or have pictures of each other on their phones.
When the staff are attaching Blobby's scooter to the car the bolt is being loosened, not tightened.
Vampires are shown to not appear in photographs. This is evident in the beginning of the film, during the wedding. Drac and Mavis do not appear in any of the pictures they take. However, later on in the movie, when Mavis is packing her things in boxes, she comes across an old picture of her and Drac, in which they are visible.but the picture she comes across is not a photo, it's a painting. you can tell by the brush marks on canvas.
When Dennis turns two years old, Drac checks his mouth for fangs, but Dennis has no teeth at all. Most babies develop their first teeth at 6 months old, so by two years old, Dennis should have had a mouth full of baby teeth. It is possible that vampires may develop teeth later than humans, which would fit in with Mavis not being considered an adult until 118. Besides, he's mentioned to be developing fangs quite late even by vampire standards.
When Dennis turns into a vampire he keeps his hair but whenever Drac or Mavis change they don't keep any of their monster features. However, this could easily be due to Dennis being part human.
As Drac dances with Mavis on the ceiling at her wedding reception, her veil still hangs down to her shoulders even though they're upside-down.
When Mavis is rapidly filling her cup with various Slurpee drinks, only the knobs of the handles move when she dispenses the drinks. The rods stay in place.
It's revealed in the earlier movies that vampires have no reflection and therefore can't be photographed or recorded on video , yet when she is clearly visible in the security camera at the mini mart .
Wayne seems a little squeamish about eating a deer in this movie when Drac is trying to bring out Dennis's inner monster , but in Hotel Transylvania , he had no trouble eating the sheep that were blocking the road .
After the zombies put the runner down on the floor , a bunch of monsters and wolf pups run across it and leave dirt ,slime and tracks all over it , but in the next shot when Johnny's family is announced , suddenly the runner is clean .
When Winnie bites Bela's hand , she bites it close to the thumb near the wrist , but it the next shot she is actually biting his thumb .
The tower that Frankenstein and the others climb is very old and rickety and considered unsafe , when Frankenstein walks to the front with the others it leans very precariously but doesn't topple over considering there is not only his weight but the weight of the others as well , but the tower topples over quiet easily when only Frank leans against the back rail .
When Johnny and Drac first start talking to Vlad , there are no balloons on the table behind them , but when Vlad starts talking about finding ways to scare Dennis so his fangs come out , suddenly there are a bunch of balloons on the table .
As Drac and the others are flying through the air on blobby , trying to beat Mavis home , the sun is beginning to rise , and when they land in the court yard of the hotel , the sun is almost completely up .
When Mavis is drinking the blue Slurpee , she completely empties the cup , but in the next shot , the cup is full to the top .
How is Mavis able to fly from California back to Transylvania without eventually running into the morning sunlight somewhere along the way .
When Dennis and the monsters are at the vampire summer camp, in one scene they are sitting by a fire. Frank was shown in the previous movie to be extremely afraid of fire, to the point of becoming scared when a match is lit near him. However, he is completely fine with the fire at the camp. A couple of scenes later, he has caught on fire and is again shown to be afraid of it.
When Mavis is seen putting Dennis to bed before the wolf party she tells Drac that Dennis goes to sleep at 8 PM, but on the sleeping chart behind her Dennis begins his free time at 8 PM.