Screams kept coming from the basement as more and more Head Priests died. They didn't even know what was happening around them as the dark mist not only blinded them but also trapped their movements.
With each scream, a fear was instilled in the other Head Priests. If they couldn't even see the enemy, how could they even attack? They hadn't seen a spell like that in the past. In fact, they hadn't even heard about this, let alone knowing how to counter that.
Since they were in closed space, the efficiency of this spell only increased as the dark mist couldn't be pushed aside. In an open setting, they could've at least countered this spell to some extent. This dark mist didn't even burn with the flames!
The only things that could be burnt were the shackles that were made with the mist, but Gabriel's vision wasn't obstructed. Whoever broke the shackles, he killed them directly, without even giving them an opportunity.