Demons are dangerous, and they suck life force energy. Sometimes they're invisible, and sometimes they manifest in human or other form. Sometimes they cross over into the human realm as vampires, while sometimes they just haunt us in our dreams.

Nightmares are filled with demons and other bad energies. Daytime demons are more subtle, and are sometimes nothing more than the guy who overcharges you for mechanical work or the person who changes a twenty dollar bill for a five.

Teens are often visited by demons in disguise because demons love to feed on teens' hormonal angst. They work on the weak, and in some myths, they capture and carry souls to Satan. In fables they present themselves as sweet fairy godmothers or little old ladies with candy. They infect the pedophile and serial killer and prey on the mentally unstable.