The Grim Adventures Of Billy and Mandy. In a nutshell the little boy Billy is an idiot, Mandy is the cruel, domineering and manipulative little girl who very rarely similes and Grim is their miserable friend-slave. The two little children are best friends and neighbors while Grim is their servant that they won in a limbo contest. Billy, Mandy and Grim reside in a make-believe town called Endsville.The trio often go on Supernatural adventures. Occasionally their friend, Irwin comes along.