The Powerpuff Girls - Quality!

I heard Malcolm in the Middle was made the same way, the show was made specifically with 4:3 aspect ratio TVs in mind to hide certain scenery elements, but when a widescreen version of the show got put on something like Netflix all of a sudden you could see things you weren't supposed to. For example a scene where Malcom says "there's no empty seats," which fit in the original 4:3 ratio broadcast, but in the widescreen version you can clearly see empty seats off to the side that older TVs would have cut off.

Before Yellow Diamond, Ms Bellum was Cartoon Network's resident non-animal giraffe.

[I specify "non animal" because My Gym Partner's a Monkey had an anthropomorphic giraffe character named Ingird]