As of Hotfix #6, the ingame tooltip for this action is inaccurate and missing key information:
The tooltip does not mention the fact that an additional attack is made against every creature within the radius of the darkness cloud.
These additional attacks also deal Weapon DamagePiercing damage, including all normal weapon damage bonuses, despite some inconsistencies in the combat log.
On-hit reactions such as Divine Smite can be applied to each creature hit by this action (at the cost of multiple spell slots, in the case of Divine Smite).
All targets within the radius of the darkness cloud are automatically Blinded, regardless of whether the attack hits them, unless they are immune to being blinded.