Place the marshmallows and butter in a large mixing bowl. Take them to the microwave and heat them for thirty seconds.
Remove the bowl from the microwave carefully and stir. If there are still whole marshmallow chunks, pop them back into the microwave for an additional twenty seconds. Stir with a spoon until all the marshmallows have melted.
Add the cereal while the marshmallow cream is still warm. Stir quickly until all the cereal is covered in marshmallows.
Grease the molds where you will form the party cups with a little oil. Spread the cereal mixture into the mold. You can apply a little pressure with your hands to compact the base of the party cups, and at the same time make a slight cavity in the center.
Put the mold in the fridge for at least two hours to cool down, and then carefully remove the mold. Put a scoop of ice cream on each party cup, decorate it with whipped cream, cherries, and colored sprinkles.