Anomaly L.A. created three limited-edition “RP-FX” cereal boxes for Reese’s Puffs that look like synthesizers and, when paired with a custom augmented reality app, allow people to create tracks in their own virtual music studio. Fans also can enter to win the “RP-PRO” — a real synthesizer designed to look like a Reese’s Puffs box, which comes with a compartment to hold cereal for snacks.