Disaster

Darth Vader kills with his sadness. He weaponized depression.

Actually, no. He weaponised anger. And suffering. There was a part in one of the Darth Vader comics where he finds Padme’s grave and meets her handmaidens that became rebels, and instead of killing them he lets them go. When he returns to Palpatine, he senses Vader’s sadness and electrocutes him to make him feel pain and anger instead, because grief won’t motivate Vader as well as rage does.