Presence for a scary character

This character has a grimoire, a book from literal hell. As i understand presence, it plays a role both in grandiosity, making yourself known, intimidation ect. but also acts as something like charisma, making impressions, and persuasion. Here is where i am at. The player has powers where the sprout wings, but these wings bust out of their chest and peel around the back in a bloody horrific display from literal hell. How would i determine this as their presence. Part of me want to give them a 5 and the other part is thinking -5. am i misunderstanding the mechanic?