This document discusses applying evidence-based medicine principles to mythical beasts. It reviews the evidence and recommendations for diagnosing and treating rhinosinusitis and unicorns. Rhinosinusitis is often misdiagnosed, with 80% of patients receiving unnecessary antibiotics. The evidence shows antibiotics only provide modest benefits for acute bacterial rhinosinusitis over symptomatic treatment. Unicorns are rarely seen and their diagnosis is difficult, while most reports indicate they are mostly harmless with treatment needs modest.