Continuity mistake: When Mr. Krabs is set on fire he runs past once with his clothes, then he runs past in his underwear, then he runs past naked, and jumps into a barrel of water. His clothes are back 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: 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 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.
Continuity mistake: After Spongebob and Patrick receive their "seaweed mustaches" they jump off the edge of the trench. When they figure out that they just jumped off the edge they look down, and directly below, the trench wall is visible with nothing on it. Yet, when they are about to hit the ground there is a branch.