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.
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.
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.
Pre-Hibernation Week / Life of Crime - S2-E13
Continuity mistake: Sandy's bikini bottom is gone as she's bending over to paint the fence.
The Secret Box / Band Geeks - S2-E14
Continuity mistake: In Band Geeks during the Day Two scene, in the beginning you can see Pearl near the front, but in the distant shot that follows Pearl has moved further back. (00:04:20)
Your Shoe's Untied / Squid's Day Off - S2-E2
Continuity mistake: Near the start, at first you can see words on the menu board, then you can't. (00:05:50)
Big Pink Loser / Bubble Buddy - S2-E3
Continuity mistake: The broom that Patrick throws on the ground in Big Pink Loser disappears soon after.
The Bully / Just One Bite - S2-E17
Continuity mistake: Just One Bite: After Squidward buries the Krabby Patty and tells SpongeBob that he hates it, when SpongeBob walks to the back door of the restaurant there's a window to the right of the door, but when Squidward makes plans to sneak a Krabby Patty that window has vanished.
The Bully / Just One Bite - S2-E17
Continuity mistake: The Bully: When Mrs. Puff enters the classroom and apologizes for being late, the door knob is at the left side of the door, but in following shots it's at the right side of the door.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: Something Smells: When SpongeBob walks into the kitchen the freezer door handle is on the right side, but when he opens the freezer door its handle is at the left side.
Dying For Pie / Imitation Krabs - S2-E6
Continuity mistake: Mr Krabs has no eyelashes when he tells Squidward not to tell Spongebob about the bomb he ate. (00:05:01)
Grandma's Kisses / Squidville - S2-E9
Continuity mistake: When Spongebob and Patrick first arrive at the crowd, there's a window on the wall next to them. After they mistake that one octopus for Squidward, the window has vanished.
The Secret Box / Band Geeks - S2-E14
Continuity mistake: In Band Geeks on day four the lever besides the big gate changes positions between pointing upwards and downwards several times.
Procrastination / I'm With Stupid - S2-E19
Continuity mistake: In 'Procrastination' when SpongeBob takes the stack of paper out of the drawer, the paper is the only thing in the drawer. In the next shot, SpongeBob pulls a pencil out of the drawer.
Answer: I believe this is the Season 6 episode "Spongicus".