In the 3rd season of Dark, the character of the Unknown is introduced. At first, every time he appears, he usually appears as three copies of himself - a boy, a middle-aged man, and an old man -, approaching a single person, and killing them.
Rather than killing certain persons whose death used to be important in one of the timelines, it seemed like he habitually killed everyone he got in touch with - why? Did he have any particular goal or strategy? For instance, why did Claudia Tiedemann's secretary at the power plant have to die? Was he just covering up traces?