The Elf on the Shelf is mischievous because it's fun! It's a way for the elf to interact with the child and bring joy to their lives. Plus, the elf is secretly watching the child's behavior, so if the child is naughty, the elf can report back to Santa. But don't worry, the elf is also very kind and loving. It just likes to have a little fun while it's watching over the child.