The pink colors on Kootie Pie's shoes, lipstick, and her bow change get more purpler and less pinker throughout the episode.
At the concert when Mario states that he "never saw so many tonsils," Toad is wearing a red jacket. In one shot where Mario and Luigi are clapping while the princess is dancing to the music, Toad's jacket is gone.
When Kootie Pie tells the musicians that she will turn them into accountants, her wand is blue. In the next shot, the wand is pink. Then when she turns them into accountants, the wand is blue again.
When Koopa tells Kootie Pie to scream, he has headphones on. In a close up shot, the headphones are gone.
On the DVD version, Milli Vanilli are clearly singing during their performances, but no voices come out of their mouths. This is because all of the licensed Milli Vanilli music has been replaced with generic instrumental music. As such, it's not a goof in the original version.
When the singers are taken by Koopa, there's a shot on the stage with three people with instruments. The keyboard doesn't have any wires or chords plugged into it.
When Kootie Pie is throwing a tantrum for not being able to got to a concert, Cheasty's head and face are brown again in one shot.
When Cheasty overhears that the Mario, Luigi, Toad, and the Princess are going to the concert, his face and head is brown when he's in the window.