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In Story Mode, when the player reaches Kamek's Library, Krag's grandson comes rushing to ask for help, as Kamek had, for unknown reasons (but possibly because he had a Sky Crystal in his possession), trapped Koopa Krag in one of his books. The player battles Kamek in Book Bash, thus freeing Koopa Krag. The old Koopa happily rewards Mario's gang with the fourth Sky Crystal. Koopa Krag owns a book that is a collectible, and according to the description, it has nine magical functions.
Koopa Krag is a brownish Koopa Troopa. He has silver hair growing over his eyes, and a silver beard growing under his chin. Most Green Koopa Troopas have have a light green shell, while Krag has a greenish-brownish shell. Like all Koopa Troopas, he has two small nostrils.