1Spray 22 regular-size muffin cups with cooking spray. In large microwavable bowl, microwave butter uncovered on High about 45 seconds or until melted.
2Add marshmallows; toss until coated. Microwave uncovered on High about 1 minute 30 seconds, stirring after 45 seconds, until mixture can be stirred smooth.
3Immediately add cereals and peanuts; stir until evenly coated. Firmly press about 1/3 cup cereal mixture into each muffin cup. Cool about 1 hour or until firm. Pipe cupcake icing on each cupcake; sprinkle with decors. Store loosely covered.