Put the Chex and Lucky Charms cereals in a very large bowl and set aside. Use the biggest bowl you have.
4 cups Chex Cereal, 4 cups Lucky Charms cereal
In a microwave safe bowl microwave the white chocolate chips, butter, and peanut butter. Microwave in 30-second intervals (you'll probably only need one minute.) Stir until the mixture is smooth and add vanilla.
1 cup white chocolate chips, 2 tbsp butter, 1/2 cup peanut butter, 1 tsp vanilla
Pour the chocolate peanut butter mixture on top of the cereal mixture and gently toss to coat all the cereal pieces. This may take a minute or two to get it spread out.
Add powdered sugar and toss to combine. You can also put the mixture in a large ziptop bag and gently shake until all the cereal is coated.
2 cups confectioner's sugar
Add the Lucky Charms marshmallows, the M&Ms, and any other candy or sprinkles you want.
2 cups Lucky Charms marshmallows, 1/2 cup green M&Ms