Spider's Little Daddy/Tricycle of Terror - S3-E1
Continuity mistake: Mandy's working on her report. The page she's on says "CORN by Mandy." A moment later, she writes the same title on another page.
The Grim Adventures Of Billy And Mandy (2001)
1 mistake in season 3 - chronological order
Hoss Delgado: Give it to us straight, Goodburger. Is our little Remus.
Mandy: Billy.
Hoss Delgado: ...Billy, on the bullet train to Smartsville, or is he riding the slow pony to the rubber forest?