Make the jalapeno syrup: Bring the sugar, 2/3 cup water and half of the jalapeno slices to a simmer in a small saucepan, stirring to dissolve the sugar. Remove from the heat and let cool completely, about 20 minutes.
Meanwhile, muddle the remaining jalapeno slices in a large liquid measuring cup with a wooden spoon. Add the pineapple juice; let sit while the syrup cools.
Strain the jalapeno syrup and pineapple juice mixture into a pitcher. Stir in the vodka, mango nectar and lime juice and refrigerate until ready to serve. Pour into ice-filled glasses; garnish with skewers of pineapple, jalapeno and mango.
Photograph by Con Poulos