Constable Training

You may deal non lethal damage with your attacks without having disadvantage on your attack.
This applies to almost every damage source, except AOE spells or spells that outright slay an enemy (it's difficult to try not to kill the poor bastard in the center of the fireball. Also, it's called Finger of Death, not Finger of Mildly Inconvenient Comma).
This represents the special training all constables receive when they join the RHC, because their supposed to apprehend threats rather than outright kill them.