1Butter 15x10x1-inch pan. Coarsely crush cereal. (To easily crush cereal, place in plastic bag or between sheets of waxed paper, and crush with rolling pin.)
2In large microwavable bowl, microwave marshmallows and butter uncovered on High 2 to 3 minutes, stirring each minute, until mixture is smooth. Stir in crushed cereal. Using buttered back of spoon or hands, press firmly in pan. Cool completely, about 15 minutes.
3Cut into shapes with 2 1/2- to 3-inch holiday cutters (such as Fourth of July flag or star, Halloween pumpkin or ghost, Christmas tree or snowman, Hanukkah dreidel or star, Easter egg or bunny, etc.). Decorate with frosting and candies.