Pour the popcorn in a large bowl (removing any unpopped kernels).
Place the white melting candy and peanut butter in a medium microwave-safe bowl. Microwave on medium power for 1 minute. Stir until melted and smooth. If needed, add additional time in 30-second increments, stirring after each time, until the candy is melted and smooth. Pour the chocolate-peanut butter mixture over the popcorn, but do not stir yet.
Add the Rice Krispies and marshmallows to the popcorn bowl. Using a large rubber spatula, gently stir to coat.
Spread the popcorn mixture on a large piece of parchment paper or a large silicone baking mat.
Place the milk chocolate melting candy in a small microwave-safe bowl. Microwave on medium power for 30 seconds. Stir until melted and smooth. If needed, heat for an additional 30 seconds. Transfer the chocolate to a zip baggie, press all of the air out of the bag and snip the corner off. Use the bag to drizzle the chocolate across the popcorn. Allow to cool until the candy coating has hardened, about 20 minutes. Break into pieces before packaging or transferring to a bowl to serve immediately. The popcorn may be stored in an airtight container for up to 4 days.