Pour the rim salt onto a flat plate. Run a lime wedge around the rim of your preferred glass. Dip the rim into rim salt mixed with a sprinkle of cayenne pepper.
Mix the mango juice, lime juice, mezcal, agave syrup, and one shake of cayenne pepper, with ice in a cocktail shaker. Shake vigorously until well chilled. Pour the cocktail into the prepared glass, with ice. Garnish with fresh mango.