Generously butter a 13x9x2-inch baking pan. Set aside.
In a large saucepan or 6- to 8-quart Dutch oven combine marshmallows and butter; cook and stir over medium-low heat until melted. Stir in 6 cups of the cereal and the walnuts until combined. Stir in remaining cereal. Transfer mixture to prepared pan. Spread evenly in pan using a buttered spatula. Cool completely.
Cut bars into 12 squares. Cut each square in half diagonally to make 2 triangles. (Or cut into desired shape.) In a small saucepan cook and stir chocolate pieces and shortening over low heat until melted.
Dip tips of triangles into melted chocolate. Sprinkle with white decorative candies. Makes 24 crisps.