Fools in April / Neptune's Spatula - S1-E19
Continuity mistake: Fools in April: While Squidward is having difficulty apologizing to SpongeBob, they're both standing in front of the pineapple with its front door wide open inward, but when Squidward places the bubble over his head the front door is suddenly wide open outward, so Squidward could slam the door.
Fools in April / Neptune's Spatula - S1-E19
Continuity mistake: In "Fools in April", Squidward put some paper towels in his ears to block out the noise of Spongebob's laugh echoing throughout the Krusty Krab. He covers his ears, and in the next shot, the paper towels are missing and not in his hands.
Fools in April / Neptune's Spatula - S1-E19
Continuity mistake: In "Fools in April", Spongebob is scrubbing the floor and a customer comes up to him to ask for a couple of ice cubes. In the next shot, the water puddle on the floor gets increasingly bigger.
Fools in April / Neptune's Spatula - S1-E19
Continuity mistake: In "Fools in April", Gary is sleeping next to his food bowl in the first shot, with Spongebob's bed nowhere to be seen. After hearing Spongebob's voice, Gary wakes up. In the next shot, Gary's food bowl is sitting in front of Spongebob's bed post.
Hooky / Mermaid Man and Barnacle Boy II - S1-E20
Continuity mistake: When Spongebob takes his outer suit/pants off and finds out that the hook is stuck through his underpants, Mr. Krabs places a Help Wanted sign up on the front door of the Krusty Krab. When Spongebob crashes onto the doors naked, the sign disappears.
Hooky / Mermaid Man and Barnacle Boy II - S1-E20
Continuity mistake: Before SpongeBob takes off his pants, his pants are the only thing that is hooked to the fish hook. Later in the scene, his underwear is hooked as well.
Hooky / Mermaid Man and Barnacle Boy II - S1-E20
Continuity mistake: In "Hooky," when Spongebob gets hooked, the hook changes from dark yellow, to dark pink, to dark blue in between shots.
Hooky / Mermaid Man and Barnacle Boy II - S1-E20
Continuity mistake: In the beginning of Hooky, there are about three boats with 3 fisherman in each. That means there would be 9, but later there are dozens.
Hooky / Mermaid Man and Barnacle Boy II - S1-E20
Continuity mistake: Hooky: When SpongeBob is hooked the pointy tip of the hook is facing out, but when he asks Krabs what he should do, the hook is hooked into SpongeBob's pants the opposite way, with the pointy tip facing him. Additionally, he's hooked at the back of his underwear and pants, but when Squidward is holding the fishing pole the hook is at the front of the underwear, which are also perfectly intact despite being ripped off SpongeBob.
Hooky / Mermaid Man and Barnacle Boy II - S1-E20
Continuity mistake: In "Hooky", Spongebob is being pulled by the hook and grabs onto a flower to try and hold onto it and it becomes limp. In the next shot, this limp flower he just grabbed has vanished.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: In "Something Smells," when SpongeBob is playing the organ at night, he turns around and his glasses are on. In 2 of the 3 shots, the glasses disappear.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: In Something Smells, when Spongebob is playing the organs at night, the level of ambient light increases dramatically between the first and second shots.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: In Something Smells, when Spongebob is making the sundae, the peanut plant vase that he throws in changes direction between shots.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: When Spongebob jumps on a car and asks "am I ugly", and the guy blows up his car, you see his car has small little wheels. When one of the wheels bounces on Spongebob, it is huge.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: In Something Smells, when Spongebob finishes eating the sundae and he comes out of the room and drops his spoon. He turns to his right, the spoon that he dropped has disappeared.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: In Something Smells, once Spongebob finishes saying hello to all the band people, he says "Is it something I said?". You see him start to walk back but when you see a close up of him, a fire hydrant appears.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: In Something Smells, when Spongebob is making the sundae, when he says "This sundae is gonna taste great" he has one spoon in his hand, but when he turns around, he has 2 spoons.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: In Something Smells, when Patrick is helping Spongebob outside with the "mirror test", he pulls out the mirror and you see his face to the side of it. In the next shot he is completely behind it.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: When Pearl gives SpongeBob the new costume for the Krusty Krab, she gives SpongeBob a mirror. In the mirror, Squidward appears and tells him not to accept the costume. If you notice, Squidward is at the LEFT of SpongeBob. Because is a mirror, in the real life he would be at the RIGHT of SpongeBob. When a shot is shown of SpongeBob and Squidward, you can see that Squidward isn't at the RIGHT of SpongeBob, he's at the LEFT.
Something Smells / Bossy Boots - S2-E1
Continuity mistake: When Spongebob is outside, and he takes out his "to do list" at first he is holding it with his right hand, but when it shows the front of the paper, you see that it is his left hand. Then it is his right hand again.
Answer: I believe this is the Season 6 episode "Spongicus".