Spy Buddies / Boat Smarts / Good Ol' Whatshisname - S5-E4
Continuity mistake: In "Good Ol' Whatshisname", Squidward is seen marking his calendar which has five weeks on it, and each row has a set of numbers. In the next shot, when it shows the rest of Squidward's jail cell, the bottom two rows of the calendar are completely blank.
Spy Buddies / Boat Smarts / Good Ol' Whatshisname - S5-E4
Continuity mistake: In "Good Ol' Whatshisname", Squidward uses a pencil to mark his calendar and sets it down on his bench when Mr. Krabs and Spongebob come to visit them. He goes up to the bars, and in a few shots, when it cuts to him, you can see the bench he was just on and the pencil has disappeared.
Continuity mistake: In the episode "Plankton's Army", there is a group of Plankton's family sitting on top of the toilet when Mr. Krabs is first shown inside it. In two shots, the group has vanished from the top of the toilet.
Continuity mistake: After Plankton blows up the Krusty Krab roof, Mr. Krabs enters the kitchen through the door leading from his office. When he opens the door, it falls off and leans against the counter beside the door. When SpongeBob approaches Mr. Krabs, the door is suddenly lying on the floor.
Continuity mistake: When Mr. Krabs walks into the kitchen after Plankton detonates the roof, the door falls off and there is no hinge attached to the door, but once Plankton has flown in through the hole in the roof, a hinge has suddenly appeared on the door.
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.
Continuity mistake: After going through the curvy air ducts, Mr. Krabs, Spongebob, Squidward and Patrick land in a metal box. In the next shot, Mr. Krabs picks up a Krabby Patty wrapper that wasn't previously there.
Continuity mistake: Patrick smashes a walkie-talkie that Squidward is holding. In a few shots, the smashed pieces that were on the ground have disappeared.
Continuity mistake: Patchy the Pirate wakes up surrounded by other people in the green room. Lincoln lifts up his hat to reveal a Spongebob plush, and Patchy points at it while lying on the floor. In the next shot, his arm is now at his side.
Little Yellow Book/Bumper to Bumper - S9-E4
Continuity mistake: In "Bumper to Bumper", Mrs. Puff gets out of the boat and asks Spongebob to switch seats with her, and Spongebob is wearing his seat belt. In the next shot, once she has made her way around the boat to the side where Spongebob is sitting, he is no longer wearing his seat belt.
Patrick's Coupon/Out of the Picture - S10-E10
Continuity mistake: In "Out of the Picture", when Squidward and Spongebob are running back to the Krusty Krab while being chased by Mr. Krabs, a shot of them entering the establishment shows an empty restaurant, but in two shots, once they've entered the restaurant, the paintings and the art expert are now inside it.
Patrick's Coupon/Out of the Picture - S10-E10
Continuity mistake: In "Patrick's Coupon", when Patrick is kicked out of the ice cream store, he is covered with ice cream. In a close up shot, he has a huge amount of ice cream on him as well as as a cherry. When it cuts to the next shot, this pile of ice cream and cherry have disappeared.
The Fish Bowl/Married to Money - S9-E18
Continuity mistake: In "The Fish Bowl", Sandy has a wristwatch on her right wrist when she first appears on the bus. When she sits near the front to observe the fish, the wristwatch has disappeared and doesn't reappear.
The Fish Bowl/Married to Money - S9-E18
Continuity mistake: In "Married to Money", Pearl cries and her tears flood Mr. Krabs' house. When this happens, he pulls a in the floor to let the water drain. In a few shots, this plug and drain are missing.
Hooky / Mermaid Man and Barnacle Boy II - S1-E20
Continuity mistake: In "Hooky", Spongebob is being pulled by the hook and grabs onto a flower to try and hold onto it and it becomes limp. In the next shot, this limp flower he just grabbed has vanished.
Krabby Land / The Camping Episode - S3-E19
Continuity mistake: In "The Camping Episode", Squidward sets down a blanket to lay under the stars and in a couple of shots, the blanket disappears.
Krabby Land / The Camping Episode - S3-E19
Continuity mistake: In "Krabby Land", Spongebob goes to check his motivational quote and from far away, the page is flipped up. But in the next shot, it is a close up and the page is flat against the stack. In the following shot, the page is flipped up again.
Pizza Delivery / Home Sweet Pineapple - S1-E5
Continuity mistake: In "Home Sweet Pineapple", Spongebob goes into Squidward's house to spend the night and sits in his bed with the pillow just the right size for him. But in the next shot, when Squidward climbs into bed next to him, the pillow has drastically grown and now both of them can lay on it perfectly.
Pizza Delivery / Home Sweet Pineapple - S1-E5
Continuity mistake: In "Pizza Delivery", Spongebob points out the antennae for the boat during his vehicle inspection, but in a few shots, when he's checking the tire pressure, the antennae has vanished.
Answer: I believe this is the Season 6 episode "Spongicus".