House Fancy/Krabby Road - S6-E1
Continuity mistake: Plankton's size changes drastically throughout Krabby Road. Plankton can be seen as reaching up to Spongebob's waist at one point. When he's clutching to the neck of a guitar, the amount of frets that go into his height change between one, two, three, and five, depending on the shot. (00:02:10)
House Fancy/Krabby Road - S6-E1
Continuity mistake: In House Fancy, Squidward gets a bad sofa injury. In the next shot, his feet seem fine.
Penny Foolish/Nautical Novice - S6-E2
Continuity mistake: In "Penny Foolish" around the beginning, SpongeBob does a lot of stunts before he picks up the penny. Then when Mr. Krabs flashbacks to what SpongeBob did, the buildings in the background change.
Penny Foolish/Nautical Novice - S6-E2
Continuity mistake: In "Penny Foolish" when Mr. Krabs is driving at night, there are a bunch of buildings surrounding him. Then when the shot cuts to the steering wheel and back to Mr. Krabs the buildings disappear.
Spongicus/Suction Cup Symphony - S6-E3
Continuity mistake: In "Spongicus" when Mr. Krabs and SpongeBob are outside looking at the "Chum Coliseum" and Mr. Krabs says "it's very suspicious" the tables inside the Krusty Krab are missing.
Giant Squidward/No Nose Knows - S6-E7
Continuity mistake: In "Giant Squidward", Squidward goes to spray his wilting kelp with fertilizer and sets down a watering can right next to him. When the kelp goes back to normal in the next shot, the watering can disappears and is not seen again.
Giant Squidward/No Nose Knows - S6-E7
Continuity mistake: In "No Nose Knows", Patrick is trying out his new nose. He passes through a cloud of perfume sprayed by a fish in front of the perfume shop. In the next shot, the fish and the perfume shop are gone.
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.
Boating Buddies/The Krabby Kronicle - S6-E9
Continuity mistake: In "The Krabby Kronicle", Spongebob takes a picture while holding the camera diagonally, but when the picture is printed, it is horizontal.
Boating Buddies/The Krabby Kronicle - S6-E9
Continuity mistake: In "The Krabby Kronicle", a smaller fish punches Larry the lobster in the gut. When they finish their conversation, they are standing in the sand. When they walk away in the next shot, they are in the road.
Boating Buddies/The Krabby Kronicle - S6-E9
Continuity mistake: In "The Krabby Kronicle", Mr. Krabs hands Spongebob his spatula next to the printing press. In the next shot, he is not holding the spatula, nor is it on the floor.
Gullible Pants/Overbooked - S6-E19
Continuity mistake: In "Gullible Pants" when Mr. Krabs is about to exit the Krusty Krab, he looks at his watch, which disappears in the next shot.
Chum Bucket Supreme/Single Cell Anniversary - S6-E22
Continuity mistake: In "Single Cell Anniversary", Spongebob places a megaphone on the ground. In a few shots, the megaphone has disappeared by itself.
Chum Bucket Supreme/Single Cell Anniversary - S6-E22
Continuity mistake: In "Chum Bucket Supreme", Patrick is painting the slogan "Krabby Patties Are Fum" on the Krusty Krab with no hole in the back of his head. In a few shots, Patrick is standing in the same spot, and the hole in his head has reappeared.
Chum Bucket Supreme/Single Cell Anniversary - S6-E22
Continuity mistake: In "Chum Bucket Supreme", Mr. Krabs hears the sound of Plankton's cash register, and the wide shot shows him standing on the pavement around the Krusty Krab. In the next shot, he is now standing in sand.
Chum Bucket Supreme/Single Cell Anniversary - S6-E22
Continuity mistake: In "Chum Bucket Supreme", Mr. Krabs notices that there are only two customers in the Krusty Krab. When he goes up to the front window, the customers and their tables have vanished.
Chum Bucket Supreme/Single Cell Anniversary - S6-E22
Continuity mistake: In "Chum Bucket Supreme", Plankton rips up a piece of paper on top of Karen. In a few shots, the ripped paper disappears.
Pineapple Fever/Chum Caverns - S6-E23
Continuity mistake: In "Pineapple Fever", while Spongebob and Patrick are protecting themselves from the elements, the nails and boards on the floor change positions in almost every other shot.
Pineapple Fever/Chum Caverns - S6-E23
Continuity mistake: In "Pineapple Fever", Spongebob re-scrambles the jigsaw puzzle right in front of him and Squidward runs outside. In two shots, when Squidward returns, the jigsaw puzzle pieces have moved to the left on the screen, almost behind Spongebob.
Answer: I believe this is the Season 6 episode "Spongicus".