Microwave the chocolate wafers and Andes mint candies together for one minute, stir, then microwave in 30-second intervals until smooth, about 2 minutes total.

In a large mixing bowl, combine the Rice Chex cereal with the melted chocolate mixture. Fold until all cereal is coated.

Transfer the coated cereal into a large Ziploc bag, add the powdered sugar, seal, and shake until evenly coated.

Pour the mixture onto wax paper and let set for about 20 minutes. Then, stir in the mint M&Ms. Store in an airtight container.