Fill a cocktail shaker with ice. Add the light rum, dark rum, pineapple juice, lime juice, simple syrup, and bitters.
Shake vigorously for 15–20 seconds, until well-chilled.
Strain into two highball glasses filled with fresh ice.
Top each with a splash of ginger beer.
Garnish with a pineapple wedge, a lime wheel, and a sprig of fresh mint. Paper umbrella optional but encouraged. ☂️