Chill everything first. Cold juice and rum mean less dilution.
Pop your pitcher and glasses in the fridge if you have time.
Mix the base. In a large pitcher, combine 1 cup light rum, 1/2 cup dark rum, 2 cups pineapple juice, 1 cup orange juice, 1/2 cup fresh lime juice, and 2 tablespoons grenadine. Stir well.
Tune the sweetness. Taste. If you like it sweeter, add 1–2 tablespoons simple syrup.
If it’s too sweet, add a bit more lime juice.
Add bitters. Stir in 3–4 dashes of Angostura bitters. It adds a subtle spice that keeps the punch from tasting flat.
Add ice right before serving. Fill the pitcher halfway with large ice cubes so the punch chills without watering down too fast.
Top with bubbles. Pour in 1–2 cups of club soda to lighten the texture. Stir gently to keep the fizz.
Garnish generously. Float orange and lime wheels.
Add a handful of pineapple chunks and a few cherries.
Serve. Pour into ice-filled glasses. Finish with a mint sprig or a light grating of nutmeg if you like.