As in what part (or parts) of a character that are terrifying in action or given thought. It can be looks, personality, ideology, and/or an ability if applied with real-life implications.
For instance, Doomfist is scary because of his ideology; the concept of using conflict to further humanity implies a never-ending wave of war where if you aren’t strong, you will suffer or die.
I think lucio dials his music up so loud that the base pushes you backward which probably ruptures everything inside your body. Lolllll. Lucio is wild and he just makes beats about it.