Monster Mix-Up is the third book in the Nintendo Adventure Books series. The book was released on July 1, 1991, and written by Bill McCay. It is notable for being the only book in the series to feature Toad as a main character, alongside Mario.
The story from the back cover:
What Has the Head of a Koopa Troopa and the Body of a Cheep-Cheep?
One of King Bowser Koopa's new mega monsters, that's what. Mario discovers that Bowser is making new and improved Koopa creations by combining Mushroom Kingdom royals with his own creepy creatures. When Mario tries to stop him, the Mario Bros. get mixed-up in ways they never dreamed possible.
As in all Nintendo Adventure Books, you control the action. Only you can make the choices that allow Mario to beat Bowser, Lemmy Koopa, and their fiendish accomplice, the Monster Mixer. Help him crack codes, solve puzzles, conquer mazes, and subdue enemies. You and Mario must outwit the Koopas at their own game—or go down in final defeat!
- 610 pts. or more – Rompin', Stompin', Wrenchmaster Supreme
- 460 to 600 pts. – Plunger
- 310 to 450 pts. – Fluid Mechanic
- 160 to 300 pts. – Plumber With Promise
- 150 pts. or fewer – Drained Brain