Pop popcorn per package instructions. Spread popped popcorn and skittles on a large baking tray.
In a small saucepan, melt butter and marshmallows over very low heat. Stir constantly.
Pour the butter and marshmallow mixture over the popcorn. Carefully stir the popcorn to coat, making sure to scoop up the skittles which will sink to the bottom of the tray.
Allow popcorn to cool. Grease hands with cooking spray or butter then form into balls of about 3 inches in diameter.