In a cocktail shaker, add lime juice, bay and sage simple syrup, mango puree, gin, and ice. Cover and shake. Strain into a tall glass with ice. Top with tonic, stir, then a splash of rum. Garnish with a fresh sage leaf by smashing it first to release the oils, then rubbing it along the rim and into the cocktail. Serve.
To make bay and sage simple syrup, heat equal parts sugar and water with several bay and sage leaves. Once the sugar dissolves, remove from the heat and cool.