Break the dry ice into large pieces using a mallet or other tool. Be careful that you use gloves when handling it, since it can cause burns if it comes into contact with your skin. Place some of the dry ice in the bottom of your cauldron. Put the remaining dry ice in a cooler nearby. Pour some hot water on top of the ice so that it starts to smoke.
Place the punch bowl on top of the dry ice inside the cauldron. Combine the ginger ale, pineapple juice, and lemon juice in the punch bowl, and stir to combine. Add scoops of lime sherbet, mix it for a few minutes until the sherbet starts to melt, then serve! Replenish the dry ice and hot water as necessary, to keep the smoke effect going.
Note: dry ice can be harmful if swallowed, so do not put it directly in the punch bowl or beverage cups.