Valentine's Day / The Paper - S1-E16
Continuity mistake: In "Valentine's Day", Patrick starts searching his present in the fair. Then he goes to a mountain and falls thinking that there will be his present. This mountain wasn't there before, even when they arrived to the fair.
Valentine's Day / The Paper - S1-E16
Continuity mistake: In Valentine's Day, almost at the end, Patrick smashes some presents with his foot. After a while, Sandy arrives with Patrick's present (a chocolate globe), and you can see that the presents have disappeared.
Valentine's Day / The Paper - S1-E16
Continuity mistake: In "Valentine's Day", SpongeBob and Patrick arrive at the fair. They watch the fair. Patrick says "You bought me a fair?", and Patrick runs to the fair. When he starts saying, "Get out of my fair.", we see that SpongeBob is closer to the fair than he was before.
Valentine's Day / The Paper - S1-E16
Continuity mistake: The Paper: The front door of Squidward's house repeatedly switches between opening at the right side and opening at the left side, and the round door knob also changes to a door handle as well, but then reverts back to the round knob.
Answer: I believe this is the Season 6 episode "Spongicus".