In large microwave-safe bowl, combine chocolate chips, peanut butter, and butter. Microwave on high power for 1 minute. Stir well. Microwave 30 seconds then stir until smooth. Stir in vanilla.
Gently mix in Chex cereal, being careful not to crush the cereal. Spoon mixture into 2 gallon-sized zip-top bags.
Add 3/4 cup of powdered sugar to each bag. Close bags and shake until well coated. Spread mixture onto waxed paper to cool completely.
When cool, combine cereal mixture, candy corn, pumpkins, M&Ms, broken pretzels, and broken Oreos in a large bowl. Stir to combine.