The Great Ghost Rescue- Eva Ibbotson

Instead of being ghastly and skeletal as a bloodcurlingly fearsome ghost, he's pink and fluffy, like a summer cloud. He longs to be like his brother, who's a Screaming Skull. Or his father, who has stumps for legs and a sword through his chest. Or even his cousins who are vampire bats. Poor Humphrey, though, can't scare anyone. But when the ghosts are in danger, it's clever Humphrey who comes up with a rescue plan...