Luke Harrison and Kelly's dad makes horror movies. One day though, he brings home a pair of identical ventriloquist dummies, Slappy and Snappy, whom he plans to use in his next movie. Luke soon finds the pair are very much alive, and Slappy's up to his usual schemes, while Snappy's there to stop him. Now, Luke and Snappy must work together to try and stop Slappy from making the Harrison family's life a living nightmare.
This book provides examples of:
- The Bus Came Back: Mr. Wood finally returns in a brief cameo during the prologue.
- Chekhov's Gun: Early on it's established there is a propane, which their drone almost bumps into. Later, Slappy bumps into it, blowing himself up.
- Don't Split Us Up: Mr. Harrison plans to seperate the dummies, which very much upsets them. They plan to get revenge on him before he can do it.
- Distant Prologue: The first section is a prologue set decades prior to set up the backstory.
- Hoist by His Own Petard: The twist reveals that Snappy was only pretending to be nice and Slappy was on it. However, Slappy is blown up after hitting a propane tank during the fight. That means he was so into keeping up the charade that he blew himself up during it. Whoops.
- Never Trust a Title: At first it's played straight as Snappy is good. Turns to be an aversion as he is actually evil.
- Present Tense Narrative: The prologue is written this way.
- Polar Opposite Twins: Slappy and Snappy, who are evil and nice respectively. Subverted when it turns out Snappy is evil too.
- Retcon: This book gives Slappy a new backstory in order to explain how Snappy exists.
- Shout-Out: Some of Mr. Harrison's movie titles are based off existing horror movie titles.
- It Came from Beneath My Bed! doubles as a reference to the film It Came from Beneath the Sea and the earlier Goosebumps book It Came from Beneath the Sink!.
- Attack of the 2000-Pound Dachshund is a reference to Attack of the 50 Foot Woman.
- The title I Married a Dummy suggests a reference to the 1958 film I Married a Monster From Outer Space.
- Spoiler Cover: The book plays with this, as the eponymous twin is nice for most of the book but the twist reveals he actually was evil the whole time.
- Stuff Blowing Up: The climax features a fiery explosion when Slappy smacks into a propane tank, which destroys most of their garage and seemingly Slappy himself.
- Theme Twin Naming: Slappy and Snappy, whose names are identical but for one letter.
