In a microwave-proof bowl, combine the chocolate chips, peanut butter, and butter. Microwave for 30-120 second at a time, stirring every 30 seconds until the chocolate chips are completely melted and smooth. Stir in the vanilla.
Pour the chocolate mixture over the Chex cereal and gently stir to coat, trying not to crush the cereal.
Pour the powdered sugar into a gallon-sized Ziploc and the brownie mix in another gallon-sized Ziploc baggie and divide the chocolate covered Chex cereal into the baggies. Seal the baggies making sure you leave plenty of air in the bags.
Shake the baggies to evenly coat the Chex cereal.
Spread the cereal out on parchment paper to let the chocolate firm up a bit, for about 20 minutes in the freezer.
In a large bowl, combine the chocolate coated cereal with pretzel balls, candy corn, Oreo pieces, Reese's Pieces, and Halloween sprinkles. Store in airtight container.
Recipe from: The Best of Life® at https://bestoflife.com