What is this thing that the Nimbus minibosses do?

You know, when they just start spewwing their magic energy around them like
It’s kind of like Aura but it doesn’t wear off.
image
Like, they clearly ain’t doing anything with it.

(my best photo with Kalliste)

Am I gonna have to do that when I reach that level?

pretty sure it’s just an inf aura that most of the bosses have