What is the story on Gustav and hilda gristle?

Gustav and Hilda Gristle are fictional characters from the animated television series "The Grim Adventures of Billy & Mandy." They are depicted as a couple of sinister and eccentric characters who run a haunted house. Their story often revolves around their interactions with the show's main characters, Billy and Mandy, as well as their various spooky antics and schemes. Their quirky personalities and dark humor contribute to the show's overall comedic and macabre tone.