Mix the cocoa powder and sugar together and place in a shallow dish.
Wet the rim of the old fashioned glass, using either water or the syrup from the cocktail cherries (I used a paintbrush). Roll the wet part of the glass into the cocoa powder mixture.
Add the mezcal, maraschino liqueur, cocoa-infused rum and bitters into a cocktail stirring glass. Add ice and stir for a minute to dilute the drink.
Add a large piece of ice to your serving glass. The size will help it to melt more slowly.
Strain the drink into the serving glass.
Place a maraschino cherry on a cocktail pick and add it to the glass for garnish. Serve and enjoy!