Pain Devil (Excruciarch)

Any creature hostile to the excruciarch that starts its turn within 20 feet of the excruciarch takes 10 (4d4) slashing damage, unless the excruciarch is incapacitated.

Magical darkness doesn't impede the excruciarch's darkvision.

The excruciarch has advantage on saving throws against spells and other magical effects.

The excruciarch gains a +1 bonus to attack and damage rolls for each creature it damaged on its previous turn.

The excruciarch makes two Scourge attacks. It can replace one of the attacks with Storm of Steel (if available).

Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage plus 13 (2d8 + 4) slashing damage.

The excruciarch swings its scourge wildly around itself. All creatures within 15 feet of the excruciarch must make a DC 16 Dexterity saving throw. Targets take 31 (6d8 + 4) slashing damage on a failed save, or half as much damage on a successful one.

As a reaction to a creature resisting damage dealt by the excruciarch, it turns its gaze on that creature, negating any resistances and immunities that creature has until the start of the excruciarch's next turn.