You Wish ('Shanghaied') / Gary Takes A Bath - S2-E11
Deliberate mistake: Spongebob gets stuck in the top of a tree as Gary removes the ladder. In previous episodes it's quite clear that he's more than willing to 'fall' as he takes no damage when hitting the ground due to the low fall speed.
Pressure / The Smoking Peanut - S2-E12
Continuity mistake: When Sandy and SpongeBob are climbing the mountain at the beginning of "Pressure," when Sandy pushes the rocks down at SpongeBob, there were two big ones holding them that vanish. You could say that she pushed them down too, but remember that they were different colours than the smaller ones. (00:01:40)
Pressure / The Smoking Peanut - S2-E12
Continuity mistake: In "Pressure" right before they all jump on land Squidward has 6 legs, but when he gets on land he has 7 legs.
Pressure / The Smoking Peanut - S2-E12
Audio problem: In the beginning of "The Smoking Peanut", Spongebob takes his hat and spits it in the air like Clamu would do. Before he puts the hat in his mouth, he says, "a cannonball", the camera is on Spongebob and his mouth isn't saying that. He has his mouth open to put the hat in his mouth.
Pressure / The Smoking Peanut - S2-E12
Continuity mistake: After SpongeBob confesses he threw the peanut at the oyster, a zoo keeper says, "wait, here is the real criminal", and he drags out Mr.Krabs. If you look at his pockets you can see food, candy, and other junk. Yet when the zoo keeper accidentally rips Mr.Krabs clothes off the pockets are completely empty.
Pressure / The Smoking Peanut - S2-E12
Continuity mistake: In The Smoking Peanut, when Spongebob and Patrick are running in to see the oyster, Patrick is on the right, but in the next shot, he's on the left.
Pressure / The Smoking Peanut - S2-E12
Continuity mistake: Patrick's popcorn disappears completely after he drops it.
Pressure / The Smoking Peanut - S2-E12
Continuity mistake: In The Smoking Peanut, after Spongebob sees Sandy he runs home. When he's trying to open the door if you look to the right the ground is completely flat and has nothing in it. Yet when Patrick comes, while he is saying, "I followed these footprints to this exact spot", there are footprints.
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 has melted from stress and exhaustion, he is trying to talk and Sandy tells him to "hold that thought", and you can see the bike that they were riding, in the background. When she makes the fly fishing joke, the bike is gone, and there is a small plane. A few shots later the plane is gone as well.
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.
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.
Pre-Hibernation Week / Life of Crime - S2-E13
Continuity mistake: When Spongebob falls off the sea needle, he lands on a fire hydrant. It shows his ripped-off skin; then it shows his back with the piece missing, but the shapes are different.
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)
The Secret Box / Band Geeks - S2-E14
Audio problem: At the end of "Band Geeks" when everyone is playing "Sweet Victory" at one point Mrs. Puff is shown playing the guitar. When this happens, you can see the others in the background not doing anything, even though their instruments are heard.
The Secret Box / Band Geeks - S2-E14
Continuity mistake: When SpongeBob is sneaking to Patrick's house, Squidwards house is missing.
The Secret Box / Band Geeks - S2-E14
Continuity mistake: When the band is marching through the streets, whilst Squidward is pressuring the flag twirlers to move faster, there are some fish drumming behind them. One is a blue fish wearing a yellow shirt seen standing on the left, and another is a brown fish wearing a red shirt seen standing on the right. When the flag twirlers behind to fly off the ground, those two fish have swapped places.
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.
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.
Answer: I believe this is the Season 6 episode "Spongicus".