Sandy, SpongeBob and the Worm / Squid on Strike - S2-E18
Continuity mistake: In "Sandy, Spongebob, and the Worm," the worm is about twice the height of Sandy and Spongebob. Near the end of the episode, the Worm charges off of the cliff and when he reaches the bottom, and smashes the town, the buildings are tiny compared to him and the sea creatures are microscopic.
Sandy, SpongeBob and the Worm / Squid on Strike - S2-E18
Continuity mistake: In Spongebob, Sandy and the Worm, when Sandy ties the worm's tongue in a knot and they run from the worm, the worm opens it's mouth but you don't see the tongue tied in a knot.
Sandy, SpongeBob and the Worm / Squid on Strike - S2-E18
Other mistake: Squid on Strike: When the destroyed Krusty Krab is first shown, the broken Krusty Krab sign has some of its letters scattered around it. There are two Ts still attached to the sign, but there is another T on the ground right next to the sign. This is impossible because there are only two Ts in "The Krusty Krab." (00:11:25)
Sandy, SpongeBob and the Worm / Squid on Strike - S2-E18
Other mistake: Squid on Strike: When Squidward looks at himself in his bathroom mirror, his buttons are on the left side of his pyjamas in the reflection. When he is shown in bed a few seconds later, the buttons are on the same side; the reflection was not reversed. (00:09:07)
Sandy, SpongeBob and the Worm / Squid on Strike - S2-E18
Continuity mistake: Sandy, SpongeBob, and the Worm: When SpongeBob makes a necklace out of the paper clip and string, he holds up the paper clip that he made into an "S" shape as he wears the necklace. In the next shot, the paper clip is facing the opposite way, then reverts back in the following shot. (00:22:20)
Sandy, SpongeBob and the Worm / Squid on Strike - S2-E18
Continuity mistake: When Spongebob shows Sandy the paper clip and a piece of string the string is very small. Yet later after Sandy says, "no silly, how about s for saving our skins", the string is a lot longer.
Sandy, SpongeBob and the Worm / Squid on Strike - S2-E18
Continuity mistake: Squid on Strike: When Squidward opens his front door and sees Mr. Krabs, he says he thought he would drop by to beg him to come back to work. Mr. Krabs is standing in the doorway in this shot, but in the next shot, he is suddenly standing inside the house, away from the door. (00:09:43)
Sandy, SpongeBob and the Worm / Squid on Strike - S2-E18
Continuity mistake: Squid on Strike: The first time Squidward opens the door to his house, the door opens to the right. Later on, when he opens it again and sees Mr. Krabs, it now opens to the left. (00:09:03 - 00:09:40)
Answer: I believe this is the Season 6 episode "Spongicus".