Evil Iggy Koopa has created a device to switch the brains of the creatures in the Mushroom Worlds. When he gives Yoshi the brain of a sinister Koopaling, Mario and Luigi jump into action. With the help of Dr. Sigmund Shrinkasaurus, they try to stop Iggy before all of their friends in Dinosaur Land lose their heads!
As in all Nintendo Adventure Books, you control the action. Only you can make the choices that allow Mario and Luigi to halt the chaos caused by Iggy Koopa's brain twister machine. Help them crack codes, solve puzzles, conquer mazes, and subdue enemies. You and the Super Mario Bros. must outwit a whole new generation of Koopa creeps- or go down in final defeat.