Spoon frosting into small resealable food-storage plastic bag; seal bag. Cut 3/8-inch tip off bottom corner of bag. Add about 1 1/2 teaspoons frosting to each cookie cup, adding a small amount to half of the cookie cup rims. Fill half with about 1 teaspoon desired cereal each, and stack another cookie cup inverted on top. Continue decorating, adding candy eyes and crushed and/or whole cereal for hair or ears, if desired.