Welcome to the Chum Bucket / Frankendoodle - S3-E2
Continuity mistake: In the episode Welcome to the Chum Bucket, when Plankton is reading a story to SpongeBob, he is interrupted. When he looks up and sees SpongeBob asleep, Sponge doesn't have his Chum Bucket Bucket Helmet on. When Plankton decides not to hit SpongeBob with a mallet and wakes him up, Sponge has the helmet on again.
Welcome to the Chum Bucket / Frankendoodle - S3-E2
Continuity mistake: Frankendoodle erases the door in SpongeBob's house (when they're fighting in the night). A few moments later you see the door is back.
Welcome to the Chum Bucket / Frankendoodle - S3-E2
Audio problem: The first time the man yells in "Frankendoodle", his mouth isn't in sync.
Welcome to the Chum Bucket / Frankendoodle - S3-E2
Continuity mistake: In 'Welcome to the Chum Bucket', the sky is constantly changing in an abnormal way. First, it is daylight when Plankton takes Spongebob into the Chum Bucket. When Spongebob starts singing, the sun is either coming up or going down. When Mr. Krabs starts singing, look through the hole in the wall and the sky looks to be about afternoon. When Spongebob and Mr. Krabs finish their song, it's nighttime.
Welcome to the Chum Bucket / Frankendoodle - S3-E2
Continuity mistake: The pencil's length in 'Frankendoodle' varies in between above and beneath the water surface.
Welcome to the Chum Bucket / Frankendoodle - S3-E2
Character mistake: In 'Welcome to the Chum Bucket', Spongebob said he likes the grill facing the wall to the right. Plankton pushes it so that it is facing the wrong wall, the wall on the left.
Welcome to the Chum Bucket / Frankendoodle - S3-E2
Continuity mistake: At the end of "Welcome To The Chum Bucket", look at Spongebob's eyes. His eyebrows are more far apart than usual, also his eyeballs are uneven a bit.
Answer: I believe this is the Season 6 episode "Spongicus".