Place cookies on cooling grid over parchment-lined cookie sheet. One day before serving, make the following colors in royal icing. Make "spooky green" with Leaf Green/Lemon Yellow and a dot of Brown icing combination. Tint remainder of icing yellow, orange and black.
For group 1 cookies, thin down all icing to a pouring consistency; but save a small amount of black for piping details. To have face with eyes and mouth blend in, you must have both background icing and black icing the same consistency and work quickly. Pour background colors over cookies; tap grid to even icing. Use full-strength black icing in cut parchment triangle to pipe eyes and mouth; let dry overnight.
For group 2 cookies, pour background color icing to cover entire cookie; tap grid to even icing. Let dry overnight. Use tip 2 and full-strength black icing to pipe eyes and mouth (smooth with finger dipped in cornstarch). Let dry 4 hours.