Something Smells / Bossy Boots - S2-E1
Continuity mistake: In Something Smells, when Spongebob jumps on the car and says "am I ugly" you see the guy holding on and he is sitting on the left side of the car, but the next shot of him, he is holding on and now on the right side of the car.
Continuity mistake: When Patrick is dressed as food for the "monster" in "Wormy," when the butterfly is on P,atrick's butt he spits out the apple in his mouth and it floats to the top of the water helmet. But when the butterfly is on his helmet, the apple is gone.
Grandma's Kisses / Squidville - S2-E9
Continuity mistake: When Spongebob stops crying, his grandma pulls a plug out of the floor to drain the water, but in a later shot through a window, the plug and hole are gone.
Your Shoe's Untied / Squid's Day Off - S2-E2
Continuity mistake: In "Your Shoes Untied", when he is in the Krusty Krab kitchen. In between shots when Squidward keeps asking Spongebob to give him the Krabby Patty, the patties on the grill disappear and reappear between shots.
Mermaid Man and Barnacle Boy III / Squirrel Jokes - S2-E4
Continuity mistake: Before he comes on his second act, there is a front shot of the crowd, you see a guy in the front with his hands up, but in the next shot, which is of his back, his hands are down.
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.
Grandma's Kisses / Squidville - S2-E9
Continuity mistake: Spongebob's watch appears and disappears between shots.
Your Shoe's Untied / Squid's Day Off - S2-E2
Continuity mistake: At the beginning of "Squid's Day Off", There is a tiny bell painted gold sitting on the opening between the kitchen and restaurant. When the shot changes, the bell disappears, then reappears when the shot changes again.
Pre-Hibernation Week / Life of Crime - S2-E13
Continuity mistake: When his pants fall off when he's trying to hide, his pants are hooked to the plant by the brown part of his pants, but when Sandy comes looking and she sees his pants on the plant, they're hooked by the white part.
Grandma's Kisses / Squidville - S2-E9
Continuity mistake: When Squidward enters Squidville, he is looking for apartment number 304. When he is looking for his apartment, the numbers on the doors disappear and re-appear.
Survival of the Idiots / Dumped - S2-E8
Continuity mistake: When the winter ends, there's a shot of Sandy's tree, and there's no window in it. When Sandy sees SpongeBob and Patrick, suddenly the tree has a window. A very noticeable mistake.
Grandma's Kisses / Squidville - S2-E9
Continuity mistake: When SpongeBob and Patrick had used the reef blower to take parts of Squidward's house off, they had taken off all parts but the two ear-like parts on the sides of the house. When Squidward demands that they put the parts back, the ear parts are no longer on the house, but are being blown back onto the house. This isn't possible because they were never taken off in the first place.
Pre-Hibernation Week / Life of Crime - S2-E13
Continuity mistake: When Spongebob and Patrick have run away, when they are fighting about the chocolate, Patrick has chocolate all over his mouth. Patrick says something like "I'll get there first" and starts running after Spongebob, and in the next shot his face is completely clean.
Grandma's Kisses / Squidville - S2-E9
Continuity mistake: When Patrick is asleep,after several scenes SpongeBob begins to cry,his Grand-mom calms him down and unplugs a plug,but Patrick is nowhere to be seen.
Sailor Mouth / Artist Unknown - S2-E15
Continuity mistake: In "Sailor Mouth" when Spongebob starts cussing in the Krusty Krab, a sailor and a pirate make a comment, but when everyone leaves the Krusty Krab, the sailor and pirate are nowhere to be seen.
Your Shoe's Untied / Squid's Day Off - S2-E2
Character mistake: In "Squid's Day Off", a wide shot shows Mr. Krabs exiting the hospital, except the building says" ENEREENCY" instead of "EMERGENCY."
You Wish ('Shanghaied') / Gary Takes A Bath - S2-E11
Deliberate mistake: Spongebob gets stuck in the top of a tree as Gary removes the ladder. In previous episodes it's quite clear that he's more than willing to 'fall' as he takes no damage when hitting the ground due to the low fall speed.
Other mistake: At the very end, Sandy puts Wormy inside of a glass jar. Not only does she break the bubble surrounding it, there's no way for water not to enter the jar as she holds it sideways. Wormy should be killed.
Pressure / The Smoking Peanut - S2-E12
Continuity mistake: In the episode "The Smoking Peanut" At the end when the man holds up the pearl out of Mr. Krabs pocket, despite being surrounded by a stadium, the close-up of his hand shows complete blue sky in the background.
Pre-Hibernation Week / Life of Crime - S2-E13
Continuity mistake: When Spongebob falls off the sea needle, he lands on a . It shows his ripped off skin, then it shows his back with the piece missing, but the shapes are different.
Answer: I believe this is the Season 6 episode "Spongicus".