Moofy is a little girl from the Invader Zim series, whose only major role is in the "The Girl Who Cried Gnome" episode.
She sells girl scout cookies, and ends up getting her foot stuck in a gopher burrow. She becomes a media attention seeker, but in the end, her foot is unplugged by Zim and is back in the arms of her parents.
She has the ability to scream at a frequency and pitch that will make Irken ships explode.