Heat oven to 350°F (325°F for dark or nonstick pans). Place paper baking cup in each of 24 regular-size muffin cups.
Make and bake cake mix as directed on box for 24 cupcakes. Cool in pans 10 minutes; remove from pans to cooling rack. Cool completely, about 30 minutes.
Meanwhile, line 2 cookie sheets with waxed paper. In large bowl, place cereal.
In 4-quart saucepan, melt butter over low heat. Add marshmallows; stir until completely melted. Remove from heat. Stir in orange food color. Pour marshmallow mixture over cereal in bowl, stirring until well coated.
For feet, place 2 gummy candies on cookie sheet. Spray inside of 1/4-cup measuring cup with cooking spray. For body, fill measuring cup with warm cereal mixture; place over feet, releasing cereal mixture and covering back half of feet. Repeat with remaining gummy candies and cereal mixture to make 24 aliens. Use 2 candy-coated chocolate candies for eyes and black decorating gel to make centers of eyes. Insert 2 pretzels for antennae.
Stir green food color into frosting container; frost cupcakes with frosting. Place 1 alien on top of each cupcake; press gently to secure. Store uncovered.