Melt chocolate chips, peanut butter, and butter together in the microwave, 30 seconds at a time, until smooth.
Spread cereal on a large baking sheet.
Pour chocolate mixture over cereal then mix with a folding motion until cereal is evenly coated.
Whisk together powdered sugar and cocoa powder in a small mixing bowl. You will need two cups total, but you can adjust the ratios to your preference. For a dark chocolate snack, use 1 cup of each. For a sweeter mix, use more powdered sugar and less cocoa powder.
Sprinkle cocoa/sugar mixture over cereal. Toss to coat.