Bake and cool brownies in 9 in. x 13 in. x 2 in. sheet pan. Use round Comfort-Grip cutter to cut brownie circles.
Ice brownies. Prepare buttercream icing following recipe directions. Tint icing royal blue/violet/black combination (for light and dark blue). Use tip 2B smooth side up and light blue icing to ice tops of brownies smooth. Reserve dark blue icing.
Decorate brownies. Use tip 4 and dark blue icing to pipe outline web as follows: Pipe lines from center to edge of brownie, 1 in. apart at edge. Connect lines with two rows of scallops, 1/2 in. apart. Position Spider-Man icing decoration at center of brownie.