First, preheat the oven to 275 degrees and line 2 large baking sheets with parchment paper.
Next, in a small microwave safe bowl, melt the butter and brown sugar. After the butter melts completely, add the vanilla. Use a whisk to combine the ingredients until they become creamy and smooth.
Then, in a large bowl, mix both cereals and the pretzels. Add the brown sugar mixture, and stir to coat.
Afterwards, spread the cereal evenly onto the baking sheets, and place in the preheated oven. Bake for 45 minutes stirring in 15 intervals.
Last, remove from oven and allow the cereal to cool completely. Add the M & M's, Autumn Mix candy, and Reese’s Pieces. Stir to combine and serve. Store in an airtight container for up to 7 days.
The calories listed are an approximation based on the ingredients and a 1/2-cup serving size. Actual calories will vary. The snack mix can be stored in a sealed container on your counter for up to 7-days.