Muddle blackberries, cucumber, and mint in the smaller half of a cocktail shaker. Add vodka, lemon juice, and simple syrup and fill with ice. Shake until well chilled, about 12 seconds. Double-strain into an ice-filled copper mule mug, pour the ginger beer down the side of the glass, and give it a gentle stir. Garnish with mint sprig.
If you choose to drink alcohol, Maine Spirits asks that you drink responsibly.
If you think you have a drinking problem, you should seek professional help.
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