Make The Crushed Ice: Wrap a few handfuls of ice cubes in a clean towel and, using a rolling pin or muddler, tap on it until all the ice is broken up and crushed.
Make The Mezcal Mule: Fill a tall glass or Moscow mule mug with ice then add the mezcal, guava juice, top with ginger beer, and a squeeze of lime. Garnish with lime slices and serve.