Mermaid Man and Barnacle Boy III / Squirrel Jokes - S2-E4
Other mistake: Squirrel Jokes: Near the end of SpongeBob's second act, he tells the crowd to give a big hand to Sandy, but to clap slowly, because she's a squirrel. Right as he says, "She's a squirrel," the holes on the bottom left of his face disappear mid-shot, then reappear. (00:20:09)
Survival of the Idiots / Dumped - S2-E8
Other mistake: Survival of the Idiots: When SpongeBob and Patrick first try to escape the tree dome, SpongeBob tries to open the door, then says that the door is slippery and frozen shut. SpongeBob's reflection is shown in the ice on the door, but it is not backwards; note the holes on his face. (00:08:43)
Survival of the Idiots / Dumped - S2-E8
Other mistake: Dumped: When SpongeBob first gets mad at Gary for spending time with Patrick, he picks him up and walks away with him. In the close-up of Gary as SpongeBob is holding him, SpongeBob's sleeve is coloured yellow instead of white as it should be. Additionally, the purple spots on Gary's shell are a lot bigger than usual. (00:17:18)
Survival of the Idiots / Dumped - S2-E8
Other mistake: Dumped: When Patrick agrees to join SpongeBob and Gary in their game of tag, SpongeBob tags him, and as SpongeBob walks away from him, his right collar leaf turns red for a frame, then the space between his tie and left collar leaf turns brown for another frame. (00:13:32)
Bummer Vacation/Wigstruck - S4-E14
Other mistake: Bummer Vacation: When SpongeBob says, "You're right, Gary. It is unhealthy to think of the Krusty Krab while I'm on vacation," his legs are missing. (00:05:55)
Have You Seen This Snail? - S4-E3
Other mistake: When Gary comes back at the end, when Gary meows and SpongeBob says, "Yeah, like that," the tears in his eyes disappear for about half a second. (00:22:50)
Someone's in the Kitchen with Sandy/The Inside Job - S7-E3
Other mistake: In the kitchen when Plankton asks, "In approximately how long do you cook a patty?" Spongebob's eyelashes are missing.
Krabby Land / The Camping Episode - S3-E19
Other mistake: In "Krabby Land", Mr. Krabs as "Krabby The Clown" finishes his short speech and goes into his office. When he slams the door, bubbles float up and those bubbles stay motionless in the air for a few frames.
Grandma's Kisses / Squidville - S2-E9
Other mistake: At the end of Grandma's Kisses, Harold "Bill" is olive green.
Chum Bucket Supreme/Single Cell Anniversary - S6-E22
Other mistake: In Chum Bucket Supreme, when Plankton is changing his sign for his restaurant, the door to the Chum Bucket is missing. (00:01:10)
Gullible Pants/Overbooked - S6-E19
Other mistake: In Overbooked, when Patrick tells Sponge-Bob about his birthday, Sponge-bob put a Krabby patty in his pants. In the next scene when you see Sponge-Bob, the patty is gone.
You Don't Know Sponge/Hide and Then What Happens - S8-E3
Other mistake: It is revealed in this episode that Patrick is right-handed. However, in the season 4 episode Krusty Towers, when asked to sign the Krusty Towers guest register, he is shown doing so with his left hand.
Other mistake: When SpongeBob has his picture taken, his tie is missing.
Other mistake: When Squidward opens the door to his house on Christmas morning, the door incorrectly overlaps the snow decoration on his house. (00:13:49)
Other mistake: During the show's introduction in Seasons 1-8, when the kids chant "SpongeBob SquarePants!" for the second time, the whole screen shifts slightly to the left. As a result, when the lyric, "If nautical nonsense be something you wish" is sung, the far right side of the screen is slightly mirrored. Note how, when any of the four boats are at the right side of the screen, they are briefly duplicated. (00:00:16)
Other mistake: Rock Bottom: When SpongeBob sets up a cardboard version of himself and is shown sneaking to the bus, his holes are missing and he is perfectly square, instead of his usual sponge-like shape. (00:18:47)
The Snowball Effect / One Krabs Trash - S3-E3
Other mistake: One Krab's Trash: When Mr. Krabs sticks the ghost drawing in SpongeBob's window with the fishing rod, the shadow of the paper is visible on SpongeBob, but there is no shadow of the fishing line holding it up. (00:17:27)
Mermaid Man and Barnacle Boy / Pickles - S1-E6
Other mistake: In the end credits for the episode "Pickles", Bubble Bass is named "BubbleBass" (without a space).
MuscleBob BuffPants / Squidward, the Unfriendly Ghost - S1-E11
Other mistake: When Squidward is on the royal bed, Spongebob's Pineapple is nowhere in sight.
Answer: I believe this is the Season 6 episode "Spongicus".