Pour black grape juice into a bundt pan or ring mold. Drop in a few grapes, blackberries, and gummy worms. Freeze for at least four hours, or overnight, until it is solid.
Place the grape juice, pineapple juice, lemonade, and soda in the fridge a few hours ahead. Cold ingredients keep the punch icy without extra dilution. Warm soda also loses its fizz fast, so don't skip this.
Pour the grape juice, pineapple juice, and lemonade into your punch bowl. Stir slowly until everything blends into one deep purple color. Taste it now and adjust the tartness with a splash more lemonade.
Stir in the black gel food coloring one drop at a time until you like the shade. Sprinkle the edible glitter on top and swirl gently. The glitter will float and shimmer like a witch's potion.
Pour in the lemon-lime soda slowly down the side of the bowl. Give it one soft stir with a ladle. This keeps the bubbles alive for longer.
Pop the ice ring out of its mold by running warm water on the outside for a few seconds. Slide it into the punch bowl. Scatter extra grapes on top and hang a few gummy worms over the edge.
If you want a black Halloween punch that is alcoholic, stir in the vodka just before serving. I like to pour it into a separate bowl. That way the kids' version stays safe and everyone can enjoy the party.
Ladle the punch into clear cups and serve it cold. Stir lightly between refills to keep the glitter moving. Top up the fizz with a little extra soda if it starts to go flat.