Bake according to package directions to make 2 (9-inch) rounds.
For the Cupcakes:
Bake according to package directions to make 24 cupcakes.
Sandwich the 2 layer cakes together with 1/2 cup buttercream. Flatten top layer by cutting if necessary, then cover the sides and top with remaining pint of frosting. Smooth out top and sides. Place in refrigerator and let chill for 1 to 2 hours.
Divide remaining 2 pints of frosting into 4 bowls. Add 1 1/2 teaspoons marshmallow flavoring to each bowl. Mix blue, red, green and yellow food coloring in each bowl. Fill 4 small sandwich bags with about 1/2 cup of each color. Cut a small slit on 1 side of the bottom of each bag and lightly pipe varying sizes of dots on the layer cake. Frost cupcakes with remaining colored buttercream frosting. Arrange and stack the frosted cupcakes in a 3-level pyramid atop the cake. Construct the pyramid with 7 cupcakes on the bottom layer; 3 on the middle layer, and 1 cupcake on top.