Unsafe and Unknown Scenarios can be defined as Critical Scenarios. Our goal is to present an approach using detailed simulation to create and find these scenarios for a given AV/ADAS system. First, we create digital twins of the world, the vehicle and the sensors. In terms of sensors, we can use detailed physics-based sensor simulation or simple sensor simulation. Then using base scenarios, we can vary these using efficient techniques to explore the DOE or Monte Carlo space. With appropriate KPI’s we then can identify critical scenarios and hence create them.