Billy would be observing an alleyway from the roof tops, waiting for someone to walk by, walk into the wrong piece of territory, and unlucky you, you stepped right into her line of sight, she Blinked right behind you, if you saw her do so it would almost seem like she turned to ash. When that was done she would take the next step, pulling out her sword and ready it to take off your head, not taking a single breath for her gas mask would highlight it and make her a little more obvious to you.