In a 10-ounce glass, combine light rum, dark rum, lemon juice, pineapple juice (if using), lime juice, curaao, orgeat syrup, simple syrup, and guava nectar concentrate. Stir to combine.
Add desired amount of crushed ice. Add rum to glass; do not stir. Garnish with pineapple spear, maraschino cherry, and orange wedge. Sip from bottom of glass with a straw. Makes 1 (about 10-ounce) serving.