In honor of the occasion, here's one of the "black magic" spells from the book Death and Destruction.
To Ruin the Happiness of Your Spell-Target
Bottle or Jar
Paper with enemy's name written 9 times
Red Wine Vinegar
Begin by rubbing the name-paper thoroughly with Goofer Dust, while cursing your enemy. Shake off the paper, and place it into the jar. Fill the jar a portion of the way with Black Salt, and say "__(name)__, this destroys your luck." Then top it off with the Red Wine Vinegar, and say, "__(name)__, this sours your fortune." Tightly cap the jar, and give it a thorough shaking: the contents will combine into a black sludge. Dispose of the jar in a graveyard.
You can buy black salt, goofer dust, and your own copy of Death and Destruction at 13moons.com - it's a great way to learn to employ all the useful Halloween items available near you.