No Weenies Allowed / Squilliam Returns - S3-E6
Continuity mistake: In "No Weeneis Allowed", Patrick punches SpongeBob's left eye, but the black eye is on SpongeBob's right eye.
The Snowball Effect / One Krabs Trash - S3-E3
Continuity mistake: In The Snowball Effect, Squidward builds his fort between his and Spongebob's house later in the ending scene his fort has moved about 30 yards away.
Grandma's Kisses / Squidville - S2-E9
Continuity mistake: Spongebob's watch appears and disappears between shots.
The Great Snail Race / Mid-Life Crustacean - S3-E15
Continuity mistake: In The Great Snail Race, Gary wipes out into the tires then fire fighters come and put him out (still near the tires) but in the wide shot Gary is back on the track.
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.
The Chaperone / Employee of the Month - S1-E12
Continuity mistake: Spongebob absorbs the pink punch making him look pink in 2 shots - one showing him squirting punch out of his nose, but a shot after that shows him yellow.
Boating Buddies/The Krabby Kronicle - S6-E9
Continuity mistake: In "Krabby Kronicle," when the female fish takes a copy of The Bottom Feeder, the pile of newspapers stays the same.
SpongeBob's House Party (aka Party Pooper Pants) - S3-E10
Continuity mistake: When Gary and Spongebob are waiting at the door, there is a sign behind him that says "pin the tail on the horace" (yes it says horace), and there is one tail hanging up, but when everybody comes in there are suddenly two.
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.
No Weenies Allowed / Squilliam Returns - S3-E6
Continuity mistake: In "Squilliam Returns", the world's smallest violin changes position between shots.
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.
As Seen on TV / Can You Spare a Dime? - S3-E5
Continuity mistake: In "As Seen On T.V", the hat on Mr. Krabs's desk has 2 lines on the anchor instead of 1.
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.
20,000 Patties Under the Sea/The Battle of Bikini Bottom - S5-E17
Continuity mistake: In one scene where Spongebob is breathing in air, you can see the container to the right is yellow, but in the scene where he's dancing around the kitchen, it turns white.
Hooky / Mermaid Man and Barnacle Boy II - S1-E20
Continuity mistake: In the beginning of Hooky, there are about three boats with 3 fisherman in each. That means there would be 9, but later there are dozens.
Help Wanted / Reef Blowers / Tea at the Treedome - S1-E2
Continuity mistake: In "Help Wanted", the last time SpongeBob says "I'm ready!", his collar turns red.
Answer: I believe this is the Season 6 episode "Spongicus".