Melt the butter glaze: In a saucepan over low heat, melt the butter and brown sugar together, stirring often until smooth and bubbling at the edges, about 3 minutes.
Stir in flavoring: Remove the glaze from heat and stir in the vanilla extract and salt until fully combined.
Mix the dry ingredients: In a large bowl, combine the Rice Chex, Corn Chex, pretzel twists and peanuts, tossing gently so everything is evenly distributed.
Pour the glaze over: Drizzle the warm butter glaze over the cereal mixture and stir with a spatula until every piece is lightly coated and shiny.
Spread to cool: Transfer the coated mix to a parchment-lined baking sheet in a single layer, so it cools evenly and stays crisp.
Let it set: Let the mix sit at room temperature for about 15 minutes, until the coating firms up and no longer feels sticky to the touch.
Fold in candy: Once completely cooled, gently fold in the candy corn and mini chocolate candies so they don't melt from leftover heat.
Portion and serve: Scoop the finished Halloween Chex Mix into bowls or zip-top bags for parties, school treats or snacking at home.