There are auras for virtually all kinds of things. Out of all of those, we seem to be missing something which could be amazing. Imagine having a aura spell, with a theme.
The name can be something cool like, I don't know, "Aura of Despair", or something simpler like "Veil".
Considering this is arguably very powerful, it should be limited to level 115+ or 125+ and sold by the shadow scholar in Arcanum. The animation of it would be a dark purply glitchy bubble, that kinda glitches in and out of existence visually, in a sort of unnatural manner.
In my opinion, this is a balanced spell that could greatly improve the QOL for shadow lovers.