Lightly grease and line a 13"x9" deep baking dish with parchment paper and set aside for now
Place a large pot over medium heat and melt 4 tablespoons of butter
Stir in 10 ounces of mini marshmallows and continue to stir until the marshmallows are completely melted and smooth
Transfer the pot off of the heat and mix in 6 cups of rice crispy cereal until everything is evenly distributed
Spread the mixture evenly throughout the parchment lined baking dish
Cover the dish with a kitchen towel and let the rice crispy treats set at room temperature until completely firm
Transfer the rice crispy treats onto a cutting board and use a sharp knife or cookie cutter to cut them into your desired shapes and sizes
Have a blast decorating little Frankenstine's, mummies, spiders, bats, pumpkins, hay bales or anything your festive heart desires!