It's school club day, and Billy, Irwin and Mandy all join different clubs. Irwin joins a macramé club, Billy a junior CIA club and Mandy the Secret Snake Club, which turns out to be merely a front for nerds to get revenge on cool kids.
Billy is ordered by Mindy to look after the Endsville school mascot, with typically disastrous results. In "Hog Wild", Billy's flagrant disregard of the rules lands him in deep trouble when he messes with his father's new motorcycle, which he has been forbidden to touch.
In "The Bad News Ghouls", when Billy's baseball team (that is playing against Mindy's own team) turns down Mandy as a new teammate because she is a girl, she has Grim disguise her as a boy named Manfred. In "The House of No Tomorrow", Billy, Mandy and Grim's outing to a character-themed amusement park goes south when they stumble upon and enter the abandoned House of Tomorrow.
In "Happy Huggy Stuffy Bears", Billy, Mandy and Grim all meet a suspicious woman named Serisue, who gives Mandy a paying job as spokesperson for the Happy Huggy Stuffy Bears, and soon, abnormal things happen. In "The Secret Decoder Ring", Billy finds a decoder ring in his cereal box which he tries to use to find the secret of the universe. However, he is not the only one trying to do it like this.
In "Wild Parts", a nose-less wizard searches for a new nose so he can smell again... and he selects Billy's bulbous proboscis for it. In "The Problem With Billy", annoyed at Billy's idiocy, Grim consults Billy's father on the subject, but he contradicts this by recounting Billy's life, in which Billy is claimed to actually be a genius!
In "Duck!", the spirit of a duck follows everyone in Endsville around making Bronx cheer noises. In "Aren't You Chupacabra To See Me?", Billy befriends a Chupacabra that lives in an enchanted VHS tape and can emerge into reality via the TV.
In "Zip Your Fly", a "wardrobe malfunction" on the part of a magic zipper causes Mandy and a fly to switch heads with one another. In "Puddle Jumping", Billy, Mandy and Grim have fun with an enchanted kiddie pool that has the power to transport them to other bodies of water in alternate dimensions.
In "The Firebird Sweet", Billy discovers a magical phoenix inside a box of Frosted Golden Apple Scraps. In "The Bubble With Billy", Billy receives from Grim some underworld gum, which must not be swallowed.