In a large microwavable bowl, mix cereal, popcorn, peanuts and pumpkin seeds; set aside.

In a small saucepan, heat butter, brown sugar, and corn syrup on high over medium-low heat until mixture is boiling, stirring occasionally; stir in vanilla pumpkin pie spice. Pour over cereal mixture, stirring until evenly coated.

Microwave 5 to 6 minutes, stirring and scraping bowl after every minute. Spread on waxed paper to cool, about 15 minutes, stirring occasionally to break up.

Stir in harvest mix. Store in airtight container.