Grease and flour a 9 x 13-inch pan. Bake cake mix according to package directions, then transfer cake to a wire rack and let cool for 5 minutes. Cut cake in half lengthwise, then make 6 corsswise cuts to create 12 beds, each 2-1/8-inch wide.
Tint 1/2 cup vanilla frosting with yellow food coloring and tint 1/4 cup chocolate frosting with black food coloring; spoon each into a small resealable plastic bag. Place 1/4 cup vanilla frosting and 1/2 cup chocolate frosting into 2 bags; set all bags aside. Spoon leftover vanilla frosting into a 1-quart glass measuring cup. Microwave on high for about 20 seconds, stirring often, until the texture resembles slightly whipped cream. Place cakes on a wire rack over a cookie sheet, then pour frosting over beds to cover. Reheat excess frosting and repour if necessary. Refrigerate frosted beds until set, about 30 minutes.
Microwave fruit-flavored candies on high to soften slightly - it should take no more than 3 seconds. Press three like colors together and roll out into a 2-1/2 x 3-inch rectangle; repeat to make 16 rectangles. Trim edges with scissors. Cut strips or small pieces from four rectangles and press on as decorations for the 12 remaining ones; set aside.
Place beds vertically on work surface. Snip a very small corner from all frosting bags; use vanilla frosting to secure pieces to each bed. Each bed should have: two cream cookies for headboard and footboard; four pirouette pieces as bedposts; one regular and one M&M's Mini on top of each post; a whole marshmallow as a pillow; a vanilla wafer for the head; and two jelly beans for slippers. Place the candy blanket over the halved marshmallows. Use remaining frosting bags to pipe hair and eyelashes onto wafers, then add a heart sprinkle for the mouth.