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)
Mermaid Man and Barnacle Boy III / Squirrel Jokes - S2-E4
Other mistake: Squirrel Jokes: At the end of SpongeBob's second act, as he tells the crowd, "Thank you, you've been a wonderful audience," he opens his eyes briefly, and they are coloured yellow instead of white as they should be. (00:20:14)
Mermaid Man and Barnacle Boy III / Squirrel Jokes - S2-E4
Other mistake: Squirrel Jokes: When SpongeBob looks in the mirror backstage after finishing his second act, the holes on his face are not reversed in the reflection (one of the holes also vanishes and reappears mid-shot). The second time his reflection is shown, they are reversed. (00:20:18)
Other mistake: At the Krusty Krab, SpongeBob tells Squidward to write a letter. Patrick then tells SpongeBob that he ripped his paper, and SpongeBob's shoes lose their colour mid-shot. (00:06:45)
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: When SpongeBob has his picture taken, his tie is missing.
Dying For Pie / Imitation Krabs - S2-E6
Other mistake: Dying for Pie: When SpongeBob seems to have exploded behind the brick wall, a brick flies out of the wall. Then, when the second explosion happens, the brick reappears in the wall mid-shot, then disappears when the wall hits the floor. (00:10:20)
Dying For Pie / Imitation Krabs - S2-E6
Other mistake: Dying for Pie: Near the end, Squidward tells SpongeBob that he spent the whole day with him doing all kinds of ridiculous things because he was supposed to explode. Right when Squidward says, "explode," a small portion of his head gets cut off briefly. (00:10:52)
Dying For Pie / Imitation Krabs - S2-E6
Other mistake: Dying for Pie: When SpongeBob trips on the rock at the end, he says, "Oops," before he even trips on it. (00:11:47)
Other mistake: At the very end, Sandy puts Wormy inside of a glass jar. Not only does she break the bubble surrounding it, there's no way for water not to enter the jar as she holds it sideways. Wormy should be killed.
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 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)
Survival of the Idiots / Dumped - S2-E8
Other mistake: Dumped: After Patrick starts playing tag with Gary and SpongeBob, Gary starts crawling around Patrick's body and does that up until it's dark out. SpongeBob is not wearing a watch on his left wrist, but then he looks at his watch, which suddenly appears on that wrist mid-shot. Then, right before he picks up Gary, the watch disappears. (00:14:06)
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)
Grandma's Kisses / Squidville - S2-E9
Other mistake: Grandma's Kisses: When SpongeBob goes to his grandma's house with Patrick, Grandma tells him to give her a kiss, and in the next shot of SpongeBob, his right leg is missing. (00:05:13)
Grandma's Kisses / Squidville - S2-E9
Other mistake: Grandma's Kisses: When SpongeBob goes to his Grandma's house with Patrick, Grandma tries to kiss SpongeBob, but SpongeBob's reflection in Grandma's glasses is not reversed; note the holes on his face. (00:05:14)
Grandma's Kisses / Squidville - S2-E9
Other mistake: Grandma's Kisses: When SpongeBob is having his "mature conversation with Patrick," he tells him, "We are supposed to be adults!" In the next shot, when the camera moves over to Patrick, SpongeBob's right hand stays visible on screen; then it vanishes mid-shot. (00:06:46)
Grandma's Kisses / Squidville - S2-E9
Other mistake: Grandma's Kisses: After Patrick sucks all of Grandma's cookies into his mouth like a vacuum, as the cookie rolls towards SpongeBob, his lower body is missing, then it appears once he moves. (00:07:44)
Grandma's Kisses / Squidville - S2-E9
Other mistake: Grandma's Kisses: After Patrick sucks all of Grandma's cookies into his mouth like a vacuum, a cookie rolls towards SpongeBob, and as he says, "It appears to be my lunch hour," a watch appears on his left wrist mid-shot, then disappears. (00:07:49)
Grandma's Kisses / Squidville - S2-E9
Other mistake: Grandma's Kisses: After Patrick bites his finger while eating the cookie, his shorts are not fully coloured in at the bottom of the screen, but they instantly are once Grandma kisses his finger. (00:08:37)
Answer: I believe this is the Season 6 episode "Spongicus".