Chill a tall glass or mason jar. Fill a cocktail shaker halfway with ice.
Add white rum, blue curaçao, pineapple juice, orange juice, and lemonade to the shaker.
Shake well for about 15 seconds until the outside of the shaker feels cold.
Strain into the chilled glass filled with fresh ice.
Garnish with lemon slices and a maraschino cherry. If using, stir in a tiny pinch of luster dust and top with blue cotton candy just before serving.
Notes
Adjust sweetness by tweaking the lemonade-to-juice ratio. Use fresh lemon juice to brighten if your lemonade is very sweet. For a lighter version, skip the rum and top with a splash of sparkling water.