Place the blackberries in a cocktail shaker and muddle them until they release their juices.
Add the gin, lemon juice, simple syrup, and activated charcoal to the shaker.
Fill the shaker with regular ice, secure the lid, and shake for 15 seconds until well chilled.
Fill four glasses with crushed ice.
Strain the mixture evenly into the prepared glasses.
Garnish each drink with a few extra blackberries and a lemon twist.