"Let's Play Impossible" (spelled as "Let's Play impossible" on the cover and inside of the book) is a storybook in the Land Before Time series. It was created by Hildy Mesnik and Barbara Slate. In this story Cera continuously does daring things to try to do the "impossible".
The book begins with Littlefoot, Ducky, Petrie and Spike playing together at a watering hole in the Great Valley. Littlefoot holds a tree down for Ducky to slide on while Spike lies in the water to help his sister climb out. When Ducky slides down the tree into the water she accidentally splashes Cera who is woken up. As Ducky apologizes to the angry Threehorn, Littlefoot suggests that Cera take a turn. Unhappy at being wet, Cera grudgingly agrees. When she gets on the tree, however, it breaks and Cera is send crashing into the water. Trying to hide her embarrassment, Cera asks to play something else.
Denying the suggestions from Ducky and Littlefoot, Cera states that she wants to do something she's never done before, something impossible. Amidst Ducky's confusion toward the statement, Cera climbs on the log of the fallen tree and brags to her friends. As they watch her in awe, Littlefoot is the only one who is worried. His worries are proven true when Cera falls off the log into the water. As her friends run to help, Cera lands on top of a clam named "Mr. Clam", who is angry at her for waking him up and blows water at her. As she spurts toward the surface, she promises herself to never show off to her friends again. Cera shoots out of the water and lands in a pool of mud. Filled with a new confidence from escaping the water, she sets off to do the "impossible" again, forgetting her promise.
Ducky suggests that she try to find their way home, and both Littlefoot and Cera point at different directions at the same time. Avioiding an argument, Littlefoot suggests that they use the twinklys (stars) to guide their way home. Cera suddenly gets an idea, and decides to try to catch a twinkly. As she climbs up the hill though, she slips and falls into a giant spider web, quickly bouncing right out. As she falls, Littlefoot reaches out and grabs her tail, while Petrie grabs her frill. As her nose brushes a glowing firefly, Cera is ecstatic that she touched a twinkly and did the impossible. In his confusion over Cera calling the firefly a twinkly, Petrie lets go of her frill and she crashes to the ground. With it being nighttime and Cera having a horn-ache, Ducky suggests that the five friends go home.
The next day the children happily play at the watering hole again, sliding down Grandpa Longneck's back. After Cera slides down Littlefoot tells her that sometimes doing the same old thing can be more fun than she can possibly imagine.
- "Leap frog" is suggested by Ducky as a game to play in this story. However, the characters in the Land Before Time series call frogs "Hoppers". In the TV series term "hopper hop" is used to describe the game.
- Likewise, the term "twinkly" is used to describe stars in this story, while the characters in the Land Before Time series are known to use the word "star". It is unknown if this is a term created by Littlefoot and his friends or a continuity error.
- Another term difference between this book and the movie/TV series is the clam being called Mr. "Clam" instead of Mr. "Snapping Shell". This could indicate that clams in the series know themselves as clams, and the term "snapping shell" is a strictly dinosaur term.
A few of the characters in this book have slight coloring differences compared to their colors in the films.
- Petrie is colored in his alternate colors.
- Grandpa Longneck's eyes are colored blue instead of red, and his back stripe goes to the tip of his snout instead of stopping between his eyes.