Shake all ingredients with ice for 15 seconds, strain into coupe. Garnish with grapefruit twist or half grapefruit wheel.
Do a split base with the Stiggins' and a white rum for something a bit less fruity. For the mango syrup, I use frozen unsweetened Goya mango fruit pulp, blended 1:1 with 1:1 cane syrup cuz it's easy and I'm cheap. You could make your own by pureeing fresh mango slices in a blender, or use more expensive mango purees like Perfect Puree, Boiron, La Fruitiere, etc.