Separate the Lucky Charms cereal from the marshmallows. Set the Marshmallows aside.
In a large bowl, combine the Lucky Charms cereal and the Chex cereal. Set aside.
Measure out the powdered sugar and optional sanding sugar into a large gallon sized zip top bag. Set aside.
In a medium microwave safe bowl, add the chocolate chips, peanut butter and butter. Microwave for a total of 1 minute, stirring at the 30 second mark. Stir until smooth.
Pour the chocolate mixture into the bowl with the cereal. Stir until the cereal is evenly coated.
Add the covered cereal to the baggie with powdered sugar. Zip the top tightly and shake until the cereal is completely covered with the powdered sugar.
Pour the cereal into a large bowl (either a new bowl or the first bowl cleaned!) and add in the Lucky Charm Marshmallows. Stir to combine.
Enjoy!! Store in an airtight container for up to 3 days.