Measure out 6 cups of rice krispies cereal in a large mixing bowl. Set aside. 

In a medium saucepan, combine the butter and marshmallows. Melt on medium-low heat until all the marshmallows are melted (with exception to a few small lumps left. This will make the bars gooey and not too dry.)

Pour the melted marshmallow mixture of the rice krispies cereal. Stir gently until well combined. 

Stir in Lucky Charms cereal. Add more if desired. 

Spread into a 9x13 pan. Cut into 24 bars. Cover with a lid or plastic wrap until you are ready to eat.