Agonarch

Eternal Suffering. The Agonarch radiates agony. Enemies within 20 feet take 10 necrotic damage at the start of their turn.

Hellish Fury. Once per combat, When reduced to 0 hit points, the Agonarch instead drops to 1 hit point and immediately makes one full Multiattack against a creature within range.

Multiattack. The Agonarch makes three Infernal Greatblade attacks. It can replace one attack with Agonizing Decree if available. 

Infernal Greatblade. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 22 (3d10 + 6) slashing plus 14 (4d6) necrotic damage.

Agonizing Decree (Recharge 6). Each enemy of the Agonarch’s choice within 30 feet must succeed on a DC 18 Constitution saving throw or be restrained by pain until the end of their next turn and take 36 (8d8) necrotic damage.

Infernal Frenzy. Once per combat, the Agonarch can choose to enter a frenzy. While in this state the Agonarch gains the following benefits:

• All Infernal Greatblade attacks are made with Disadvantage, but heal for half of the damage dealt.
• The Agonarchs AC increases by 1 for each creature within 5 ft. of it.
• The Agonarchs critical range is increased to 18-20.