Velma puts her human comet helmet above the glasses, which disappear as soon as her eyes can be seen through the helmet's.
When Shaggy and Scooby are hiding in the popcorn cart, the gang is clearly a few yards away. When the duo turn around, revealing the werewolf to the left, the gang disappears.
When Marius introduces Fred to Oliverio and Lena, Daphne is wearing her circus outfit, but when Marius takes her to Schmatko's trailer, she is wearing her casual clothes.
Shaggy thinks that Australia is a made-up place, despite having been there in Scooby-Doo and the Legend of the Vampire (2003) and Reef Grief! (2005), among other occasions. In the vampire movie, he met kangaroos, yet now he thinks they are mythical creatures.
Daphne is portrayed as being a good unicycle rider since childhood, but in Bedlam in the Big Top (1969) she had no idea how to ride one.