I always make sure my soda and pineapple juice are cold before I start. Warm soda loses its fizz fast, and nobody wants a flat punch sitting on the table. Pop both in the fridge a few hours ahead, or use ice packs in a cooler if you're short on time.
Start by pouring the pineapple juice into your punch bowl, followed by the lemon-lime soda. I pour slowly down the side of the bowl instead of straight down the middle, which keeps the soda from fizzing over and losing carbonation too quickly.
If I want that extra spooky glow, I add a few drops of green food coloring right into the liquid at this stage and give it a light stir. Skip this step entirely if you're happy with the natural pale color from the sherbet.
Using my ice cream scoop, I add rounded scoops of lime sherbet right on top of the liquid. I don't stir it in completely — I like leaving some scoops whole so they float and slowly melt, creating that bubbling cauldron effect.
This punch tastes best fresh, so I make it as close to serving time as possible. I set out a ladle so guests can scoop up both the liquid and a bit of melting sherbet in every cup.