Combine strawberries, watermelon, sugar, and water in a small saucepan. Bring to a gentle simmer over medium heat, stirring occasionally until the fruit breaks down and sugar dissolves, about 6–8 minutes.

Remove from heat and stir in 1 tablespoon fresh lime juice. Let the mixture cool for 10–15 minutes.

Blend the cooled fruit mixture briefly (1–2 pulses) to homogenize, then strain through a fine-mesh sieve into a jar or container, pressing on solids to extract as much liquid as possible. Discard solids. Chill the syrup until ready to use. Syrup will keep in the refrigerator for up to 7 days.

Cocktail Assembly

Fill a cocktail shaker halfway with crushed ice.

Add 2 oz light coconut rum, 0.5 oz dark aged rum, 1 oz chilled tiger's blood syrup, 3 oz fresh pineapple juice, 0.5 oz fresh lime juice, and 0.25 oz orange liqueur (if using) to the shaker.

Add 2 dashes of Angostura bitters.

Secure the shaker lid and shake vigorously for 10–12 seconds until the outside of the shaker feels cold and slightly frosted.

Fill a highball or tiki glass with crushed ice (about 3/4 full). Double-strain the shaken mixture over the ice to remove small ice shards and any pulp.

If desired, float an extra 0.25 oz dark rum on top by pouring it slowly over the back of a spoon to create a layered look.

Garnish with a pineapple wedge and a maraschino cherry on a pick. Serve immediately with a straw.