Shock is one of the three Trick-or-Treaters, "one of Oogie's boys" as the Mayor says, even though she is a girl. But just like Lock and Barrel, she shows no actual allegiance to Oogie Boogie or to anyone else. They all go to where it seems the most fun to cause trouble.
She is the oldest, being seven years old and only slightly taller than Lock, though her hat makes her a lot taller. She's the most cunning and intelligent of the trio, coming up with the plan on how to kidnap "Sandy Claws".
On their first try they mistakenly take the Easter Bunny instead, which angers Jack, and are told to take the frightened Holiday Spirit back to his own world. They succeed on the second attempt on bringing "Sandy Claws" to Jack.