The Graveyard Shift / Krusty Love - S3-E13
Continuity mistake: In "The Graveyard shift", Squidward begins to count the signals that means the ghost will appear. "First the lights, then the phone.", and a green slime appears in the wall. Squidward says "Oh, wait, they always do that, but what was the third thing?", and the bus appears at the front of the Krusty Krab. SpongeBob says, "I didn't know the bus comes here at this hour", and look at the wall: the green slime has disappeared.
The Graveyard Shift / Krusty Love - S3-E13
Continuity mistake: When Squidward sees the "ghost", he gets so frightened that hair comes out of his head and his job's hat falls off. In the very next shot, the hair is gone, and the hat is there again.
The Graveyard Shift / Krusty Love - S3-E13
Continuity mistake: In "Graveyard Shift," when Squidward says to that guy they think is the hash-slinging slasher, "If that was you on the phone and you on the bus, then who was flickering the lights?" look at the "order here" sign. It says "order hear" instead of "order here," which it reads in previous shots during this episode.
The Graveyard Shift / Krusty Love - S3-E13
Continuity mistake: When SpongeBob is cleaning the roof, you can see that there isn't nothing up there. The very next shot shows a closer view to SpongeBob and we can see that is a bucket there. That wasn't there before.
The Graveyard Shift / Krusty Love - S3-E13
Continuity mistake: In 'The Graveyard Shift' Squidward explains that there are three signs concerning the arrival of the Hash-Slinging Slasher. He then holds up three hands. In the next shot, he is only holding up one hand.
The Graveyard Shift / Krusty Love - S3-E13
Continuity mistake: Graveyard Shift - Sometimes the kitchen walls are light green, and sometimes they are dark green.
Answer: I believe this is the Season 6 episode "Spongicus".