Pour the vodka, watermelon puree, lime juice and Simple Syrup into a pitcher. Add to a punch bowl or a hollowed-out watermelon. Serve in punch glasses over ice and garnished with mint.
Combine the sugar and 1 cup water in a small saucepan and bring to a boil. Cook, stirring, until the sugar dissolves. Remove from the heat and let cool completely. Keep covered in the refrigerator for up to 1 month.