During the song "Happy Birthday, Jim" at the beginning, Rainbow the Clown puts a crown on Jim. In later shots, Jim is no longer wearing the crown.
When Rainbow the Clown transforms into Mr. Mime after getting hit by bleach spilling out of the bleach truck, the first part of his body to become black and white while in the process is at his shirt area. When the camera goes to his head and shirt, his shirt is back to being colorful before becoming black and white again with the rest of his body.
When Bubbles shows a drawing of herself and her sisters as they're riding the school bus, the drawing is first shown being solidly colored, and she and her sisters in the drawing have no shoes or socks on. When the camera changes to a close-up of the drawing, the picture has zig-zag colors and the girls have shoes and socks on in the pic. When the camera angle changes once again, the drawing's colors are back to solid and the girls in Bubbles's drawing have on socks but no shoes.
When Mr. Mime casts a black-and-white effect when the camera shows the baby and its mother, it is coming from left to right; but when the camera zooms out, he is to the right of the mother and her baby.
Certain objects in Townsville are not properly grayscaled when under Mr. Mime's effect where some may use the wrong shade or tint versus the colors they're transformed from.
During the final shot of the transformation process from Rainbow the Clown to his alter-ego of Mr. Mime, he changes his stance before the progression finishes.