Heat oven to 350 degrees F. Grease a 9 x 13-inch cake pan. Prepare cake mix according to package directions. Pour into prepared pan, and bake 33 to 38 minutes, until toothpick inserted in center comes out clean. Cool in pan 15 minutes, transfer to wire rack, and cool completely. Cut crescent shape lengthwise from cake to create moon. Place moon on serving platter.

Heat oven to 350 degrees F. Prepare cookies according to package directions for cut-out cookies, and sprinkle about 1/4 cup flour onto work surface. Coat both sides of cookie dough with flour. Roll out, using additional flour as needed to prevent sticking, and cut out 12 three-inch stars. Bake 12 minutes, cool 1 minute, and transfer to wire rack; cool completely.

Tint 1/2 cup vanilla frosting light blue. Spoon into small resealable plastic bag, and snip off corner. Tint frosting remaining in can bright yellow. Divide frosting from second can between 2 bowls. Tint 1 bowl royal blue. Spoon 1/2 cup vanilla frosting from second bowl into a resealable bag. Snip corner of bag.

Spread the remaining vanilla frosting in bowl over top and sides of cake in the shape of a nightcap. Frost remaining top and sides of cake with yellow frosting. Using light-blue frosting, pipe decorative lines over nightcap. Pipe dots along the border of the cap. Using brown decorating icing, pipe outline of nose, mouth, and closed eye. On serving plate, pipe out Z's in gradually smaller sizes next to the cake.

Spread thin layer of royal-blue frosting over star cookies. Using the vanilla frosting in the bag, pipe a thin outline around each cookie.