The Book of Spells is the Glooms' go-to guide on magical spells. In "For the Love of Cheese" when Hildy consulted it to find a cure for Grim's frog-turning spell, but her search turns up nothing. It also appeared in "Knick Knack Paddy Whack" when Grim searched for a way to open up the Pearl of Wisdom while Hildy tried various methods to do it; the book's recommended action is to say the "magic word".
In "For the Love of Cheese", the book's cover includes an image of a large eye with a red iris above a potion-filled cauldron with two flasks pouring liquids into it and drawings of a bat, a skull, a cat and a spider on its four corners, while in "Knick Knack Paddy Whack" its cover include an illustration of a hand with the red iris. In its first appearance (by production code) in "For the Love of Cheese", the Book of Spells is a giant book, but in "Knick Knack Paddy Whack", the book is normal sized.