Continuity mistake: In the scene where Mindy is showing Spongebob and Patrick "Planktopolis," it shows a large fully-built statue of Plankton. A few seconds later the right side of the head is shown missing and still being worked on.
Continuity mistake: When Spongebob and Patrick approach the county line, they meet the two laughing fish; one is short and fat, one tall, thin and has two patches on his knees. These patches disappear in one shot; when the short fat one is bouncing on the other one's stomach and they're both laughing.
Continuity mistake: When Spongebob runs through the skulls to get to the Free Ice Cream Booth, a skull and bones fly out and land in front of the Patty Wagon. Two shots later though, they're gone.