Melt butter in a large saucepan over medium heat. Stir in marshmallow creme and peanut butter. Cook, stirring often, about 2 minutes. Remove from heat.
Stir in the brown rice cereal until evenly coated.
Coat a 13 x 9 inch baking dish with cooking spray. Press the cereal mixture into the dish until evenly spread out. Top with the M&M’s, pressing them into the top of the cereal mixture.
Melt dark chocolate chips in a microwave-safe bowl in the microwave, stirring every 30 seconds until completely melted. Drizzle over the cereal mixture. Repeat the same process with the butterscotch chips.
Refrigerate, uncovered, about 20 minutes or until the cereal mixture is set and hardened. Slice into 16 squares and serve.