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You can see these how tos in video form here:
You'll need a 16 oz bag of mini marshmallows, 2-5 tablespoons water, and a 2 lb bag of powdered sugar.
add the water to the marshmallows and microwave for 2 minutes.
stir until you have no lumps.
introduce the entire bag of sugar into the marshmallow mixture. Knead until you have a play dough like blob. refrigerate for 15 minutes to firm.
take small portions and color them with food coloring.
roll your fondant till it's 1/4 of an inch thick and and long and as wide as your cakes chosen dimensions. apply to your cake. Make sure you have a layer of buttercream between the fondant and your cake.