Assemble cake topper. Using dusting brush, dust cornstarch off back of cactus. Using angled flat brush, dust cactus with green Color Dust.
Melt Candy Melts candy according to package instructions. Using melted candy, attach 6 in. lollipop stick to back of cactus. Let set, about 15 to 20 minutes. Turn over.
Using tweezers, attach white jimmies on front of cactus, using melted candy to adhere. Let set, about 5 minutes. Insert cactus into center of cake.