What is nightmare cartoons?

As an AI language model, I don't have personal opinions, but I can provide information on the subject.

Nightmare cartoons refer to animated shows that feature scary or horror themes, characters, or imagery. These cartoons often target an older audience as they contain mature content, including violence, gore, and adult language. They are often used as a form of entertainment for people who enjoy horror movies and stories. Some popular nightmare cartoons include "Courage the Cowardly Dog," "Invader Zim," "The Grim Adventures of Billy and Mandy," and "Aaahh!!! Real Monsters." These cartoons can be enjoyed for their unique art style, humor, and suspenseful plotlines. However, they may not be suitable for young audiences due to their dark and mature themes.