Place the 4 cups of ice in a large pitcher. Pour in the ginger beer, vodka, cranberry juice, and freshly squeezed lime juice.
Stir thoroughly until the liquids are evenly blended and the mixture has become lightly chilled.
If desired, add fresh ice to individual copper mugs.
Pour the prepared cranberry Moscow Mule mixture from the pitcher over the ice, distributing it among the mugs for serving.
Decorate each drink, if desired, with a rosemary sprig, a slice of lime, and several whole cranberries.
Serve the cocktails immediately while cold and freshly mixed.