Mandy (voiced by Grey DeLisle) is a girl about Billy's age who has a morbid, cynical and merciless attitude. Unlike Billy, she is more stable, sane and intelligent. She hates everything, especially unicorns. She will nag, punch, or otherwise injure (physically, emotionally, mentally or any combination of the three) anyone who gets in her way. She is Billy's "best friend" regardless of the awful way she treats him. She orders Grim and Billy to do chores for her, among a slew of other grunt work.