Prepare the cereal. Place the Rice Chex cereal in a large mixing bowl and set aside.
Make the chocolate coating. Combine the chocolate chips, peanut butter, and butter in a microwave-safe bowl. Then, microwave on high for 90 seconds, pausing halfway to stir. Once fully melted, stir until smooth.
Coat the cereal. Pour the chocolate mixture over the cereal. Gently fold with a spatula until all pieces are evenly coated.
Shake with powdered sugar. Add the powdered sugar to a 2-gallon resealable plastic bag. Transfer the chocolate-coated cereal into the bag, seal it tightly, and shake vigorously until all pieces are evenly coated. If you don’t have a 2-gallon bag, divide the cereal and powdered sugar into two smaller bags and shake them in batches.
Cool the mixture. Spread the coated cereal on a sheet of wax paper or parchment paper. Let it cool for 5–10 minutes.
Add mix-ins. Once the coated cereal is cool, transfer it back into the plastic bag or a large bowl. Add the Valentine’s M&Ms, frosted animal crackers, and sprinkles. Shake or stir gently to combine.
Serve and enjoy. Transfer the mixture to a decorative serving bowl or portion it into individual Valentine’s-themed gift bags for a festive touch.