Revealing mistake: After Roger reads Marvin Acme's will out loud, all of the toons start jumping for joy. Meanwhile the music machine is still activated in the background, and its colorful flashing lights are being reflected on the ground near Betty Boop and Tweety at the front of the crowd. With all of the toons grouped together like they are, the machine's colorful lights should have been obscured, not reflected. (01:35:30)
Revealing mistake: During the Toon Patrol chase, before the cab enters the alleyway there's a wide shot of the cab making a fast turn. Valiant has his head down, with his hat covering his face and his body totally motionless, opposite to what he looks like in the close-ups where he is grabbing the steering wheel, his head up and controlling the car, thus revealing that the actor was replaced by a dummy in some of the shots. (00:58:40)
Revealing mistake: When Eddy is fighting Judge Doom, Eddy is holding a giant cartoon magnet. He then attracts Judge Doom's sword and when Eddy drops the magnet it is attracted to a steel drum. If you look at the bottom of the drum you can see two strings on the bottom of the drum as it moves towards Bob Hoskins. (01:27:10)
Revealing mistake: When Roger takes a shot of bourbon and blows his top, it causes most of the glass objects in R.K. Maroon's office to bust into pieces. In some instances you can see an explosive charge breaking the glass - like the giant angel statue at the center of R.K.'s trophy collection. (00:24:00)
Revealing mistake: The streetcar railway tracks are simply metal strips laid in the road. When Eddie jumps off the back of the streetcar's bumper, you can see that the rails are not in full contact with the road, as there are visible gaps between the rails and the road surface. What's more, the rails do not have the grooves that would be necessary for the cars' wheel flanges. (00:10:10)
Revealing mistake: During the climax, one of the weasels says "Toon Town's right on the other side of the wall, boss!" If you look, you can see a brick moving completely by itself behind him. It literally just pushes out of the hole in the wall as though it's being pushed from the other side. It seems like the other weasel was supposed to be animated pulling it out, and they somehow forgot to animate that part. (He does reach over and grab it for a split second... but then immediately lets go for some reason).
Revealing mistake: Eddie heads into Toontown with an oversized animated gun. As he lurks into an alley, his gun is a plastic prop. During filming, Hoskins would carry the prop gun and the animated gun would be superimposed over it, but the animation wasn't applied to the gun in the alley. (01:13:50)