Weird Mob i couldn't find

[IceJay13]

So in a Simply magic World i have there is a mob near my base that causes fog and i have no idea what mob this is. I even checked most of the spawn eggs in creative in a new world. does anyone know what mob it is and if i should avoid it.

 

[GamerwithnoGame]

It's very likely to be an Eldritch Guardian from Thaumcraft. Does it look like a robed, hooded figure?
If not, it may be something I'm unfamiliar with.