Scaredy Pants / I Was a Teen-age Gary - S1-E13
Continuity mistake: The Krusty Krab is filled with Halloween decorations during the episode, but when Spongebob jumps to hide in a barrel there are no decorations in sight.
Scaredy Pants / I Was a Teen-age Gary - S1-E13
Continuity mistake: When Spongebob agrees to hear Mr. Krabs' story, their seats come out of nowhere.
The Secret Box / Band Geeks - S2-E14
Revealing mistake: When Squidward asks who has played instruments before and Plankton responds, look at Plankton's triangle. The bottom disappears for a split-second.
Selling Out/Funny Pants - S4-E5
Continuity mistake: In "Selling Out", Mr. Krabs hears the footsteps of many customers approaching and the shot shows the entrance to the Krusty Krab from the inside, with no one in sight. When Mr. Krabs tells the guys that they're coming, it shows Squidward in a few shots mopping right in front of the doors, even though he wasn't seen there previously.
Continuity mistake: Plankton is questioning Mr. Krabs and SpongeBob for the formula whilst they are stuck inside a mechanical hand. The area where the screw is located can be seen on both sections of the hand, on the right and left hand side. In some shots the right side of the hand completely obscures the screw on the left side, and in some shots not. Also, in one shot, the screw changes colour and becomes white.
Patrick's Coupon/Out of the Picture - S10-E10
Continuity mistake: In "Patrick's Coupon", after Patrick is released from the crane, he suspects two male fish of wanting to steal his coupons. Next, he hears two female fish talking and thinks they want his coupon too. When he goes to talk to them, the guys he was just talking to have disappeared. In two shots, the male fish reappear.
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.
Selling Out/Funny Pants - S4-E5
Audio problem: In "Selling Out", Mr. Krabs explains to Spongebob that he's retiring. When he says "bowls of fruit", his mouth doesn't match the movements.
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.
Answer: I believe this is the Season 6 episode "Spongicus".