Melt 9 tablespoons of the butter in a large pot over low heat. Add 3 packages marshmallows and heat, stirring, until completely melted. Add the chocolate-flavored rice cereal and stir until well coated. The mixture will look very white because of the melted marshmallow; that's okay because the color will fade. You can add a dash of cocoa powder to deepen the color if you'd like.
For the hat base: Grease a large piece of parchment with butter. Oil your hands so the cereal doesn't stick, then remove about a quarter of the cereal mixture. Press and mold the mixture on the greased parchment to create a 10-inch flat circle.
For the hat: Build the remaining cereal mixture into a cone with a 6-inch-wide base. Set the cone on top of the hat base. Shape bends and divots into the cone to make a realistic looking hat.
Melt the remaining 3 tablespoons butter in a saucepan over low heat. Add the remaining package of marshmallows and heat, stirring, until melted. Stir in the plain rice cereal until well coated. Grease a small bowl with butter and transfer 1/2 cup of the cereal mixture to the bowl. Set aside.
For the hatband: Add a few drops of green gel food coloring to the rest of the cereal mixture in the saucepan and mix well until the color is even. Using the green batch, create a 3-inch-wide band or strip to wrap around the entire base of the cone.
For the buckle: Dust the reserved batch of cereal mixture with edible gold powder and shape into a square buckle. Press the buckle onto the base of the hatband. If the mixture doesn't hold its shape, let it set for 10 minutes to stiffen.
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