Line a large rimmed baking sheet (or two medium sheets) with parchment paper or a silicone baking mat to prevent sticking and make cleanup easier.

In a very large mixing bowl, combine the popped popcorn, small pretzels, rice or corn Chex cereal, mini marshmallows, candy corn or mellowcreme pumpkins, and roasted peanuts or pumpkin seeds (if using). Gently toss until evenly distributed. Discard any unpopped popcorn kernels before mixing.

Add the white chocolate chips (or candy melts) and butter or refined coconut oil to a microwave-safe bowl. Microwave on 50% power in 30-second intervals, stirring after each burst, until smooth and fully melted (about 1 1/2–2 minutes total). Stir in the fine sea salt and vanilla extract, if using. If the mixture is too thick, add an extra teaspoon of oil.

Pour about two-thirds of the melted white chocolate over the popcorn mixture. Use a large spoon or spatula to gently fold and toss, coating as much of the mix as possible without crushing the ingredients. It is fine if some pieces remain uncoated for a varied sweet-and-salty texture.

Spread the coated mixture onto the prepared baking sheet(s) in an even layer, avoiding a tight mound. Drizzle the remaining white chocolate over the top in thin zigzags to help create clusters.

While the white chocolate is still wet, sprinkle the Halloween-colored M&M’s (or similar candies) and candy eyeballs evenly over the top. Gently press a few eyeballs into larger clusters so they are visible.

Allow the mix to sit at room temperature for 30–45 minutes, or until the white chocolate has fully hardened. If your kitchen is warm, place the tray in the refrigerator for about 15 minutes to speed up setting.

Once the chocolate is set, break the monster munch into large clusters. Transfer to a big serving bowl, smaller bowls for a snack table, or portion into treat bags for gifting or parties.