It’s cannon that demigods can wield the mist, especially Hecates children.
Do you think Alabastor C. Torrington would use the mist to traumatize little children when they stare at him for too long, and appear as a elderitch creature for a few seconds.
Like imagine being a little Kid, Some brunette walks in the aisles and you don’t realize you’re staring at him, but he turns around and he looks like a doppelgänger from Mandela catalog .
You turn around to tell your parents the horror you witnessed, but the moment you 180 to point out the entity, its like it was never there.
There you have it, my head cannon of our magic boy.