Sandy's Rocket / Squeaky Boots - S1-E8
Continuity mistake: In "Squeaky Boots", a piece of Mr. Krabs's foot comes off in a hole in the floor boards. Several shots later, it disappears by itself.
Sandy's Rocket / Squeaky Boots - S1-E8
Continuity mistake: In "Squeaky Boots", Mr. Krabs is about to reach a curve in his boat, but in the next shot, he continues driving straight.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: When Spongebob goes to answer his door, Patrick was obviously in front of the door. After Patrick says, "Spongebob doesn't like me anymore", it cuts to a different shot to show the outside of the front door, and Patrick has moved to the side of the door.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: Opposite Day: The front door knob on Squidward's house repeatedly switches between the left and right side of the door, so it opens the opposite way (it has nothing to do with it being opposite day).
Nature Pants / Opposite Day - S1-E9
Continuity mistake: In "Opposite Day", Spongebob pushes Squidward through the sand, leaving a pile of sand. Two shots later, they are now on Spongebob's sidewalk and the sand pile has disappeared.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: In most of the show, Squidward's house only has windows on the front of his house. But, in "Opposite Day", he has windows on the "ears" of his house, which don't appear throughout the show.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: In "Nature Pants", Spongebob comes back home, where his friends have thrown a "Welcome Back" party for him. When he enters, two balloons float behind him. In the next shot, they disappear.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "F.U.N.", Mr. Krabs sets down the Krabby Patty in front of Plankton. Almost the whole plate is on the yellow part of the table, but when the camera cuts to Plankton, the plate is mostly in the red part of the table. In the next shot, the plate returns to its original position.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "F.U.N.", Plankton uses a laser to get through the secured Krusty Krab. When he does this, we can see the outside. In the next shot, the hole is now gone.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "Culture Shock", Mr. Krabs arrives in a wheelbarrow of money, with several bills landing on the floor. In a few shots, the money has disappeared.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "Culture Shock", Squidward is waiting next to a slightly opened curtain. In the next shot, the curtain is completely closed.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "Culture Shock", Squidward closes the curtains, leaving a pile of rope, and Spongebob comes down from the ceiling. In two shots, the pile is gone.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "Culture Shock", Patrick is sitting at a table with Spongebob's parents and Mr. Krabs, who each have a plate and silverware. When the camera cuts closer to Patrick, his plate and silverware have disappeared. His plate and silverware reappear in another shot.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: When we first see Squidward in the canyon background, his outlining is gone. Then, in the next shot, it's back.
MuscleBob BuffPants / Squidward, the Unfriendly Ghost - S1-E11
Continuity mistake: When Squidward comes out of the bathroom and sees his melted sculpture, the eyes on the melted sculpture change from looking on the floor to looking up in a matter of seconds.
MuscleBob BuffPants / Squidward, the Unfriendly Ghost - S1-E11
Continuity mistake: When Patrick throws Squidward the watermelon, it lands on his torso and he falls down. When the camera goes back to Squidward, the watermelon is in his mouth.
The Chaperone / Employee of the Month - S1-E12
Continuity mistake: When Spongebob is talking about Annoy Squidward Day, you see a calendar with 28 days, indicating that it's February, but the empty picture on the wall says January.
The Chaperone / Employee of the Month - S1-E12
Continuity mistake: When Spongebob, in his black suit and long legs, is at the door of Mr Krabs', he used a lever to lower himself down. When we cut back to Spongebob, it's gone.
The Chaperone / Employee of the Month - S1-E12
Continuity mistake: When Spongebob is crying next to the employee of the month wall, (just before he says "How could I have let the quality of my work slip so much?") the order of the pictures is messed up. It goes December, February, January. Then, when we see the close-up of Squidward's face laughing, the order is correct again.
The Chaperone / Employee of the Month - S1-E12
Continuity mistake: In "Employee of the Month", when Spongebob is spying on Squidward, Squidward puts his alarm clock to the left of his bed. When Spongebob tries to get the clock, it is now to the right of Squidward's bed.
Answer: I believe this is the Season 6 episode "Spongicus".