Aura of Murder. As long as Sarevok is not incapacited, hostile creatures within 5 feet of him gain vulnerability to piercing damage unless they have resistance or immunity to such damage.
Devastating Critical. On a critical hit, Sarevok deals an extra 2d6 necrotic damage.
Magic Resistance. Sarevok has advantage on saving throws against spells and magical effects.
Legendary Resistance (2/Day). If Sarevok fails a saving throw, he can choose to succeed instead.

Multiattack. The warlord makes two weapon attacks or one weapon attack and use its Deathbringer Assault if available.
Sword of Chaos. Melee Weapon Attack: +11 to hit, reach 10 ft., 1 target. Hit: (2d8 + 8) slashing damage. The target must make a DC 13 Constitution saving throw or take 1d6 necrotic damage and its maximum hp is reduced by the same amount. Sarevok regains the same amount of hp. A successful save negates the extra damage and the reduced hp.
Deathbringer Assault. (Recharge on 5-6). Melee Weapon Attack: +11 to hit, reach 10 ft., 1 target. Hit: (2d6 + 6) necrotic damage. The attack is a critical hit on a roll of 18, 19 or 20 on the roll. Any creature that you hit with this attack can't regain hit points for 1 minute. The target can make a DC 13 Constitution saving throw at the end of each of its turns, ending this effect early on a success.
Stunning Gaze. Sarevok targets one creature it can see within 30 feet of it. The target must succeed on a DC 13 Wisdom saving throw or be stunned until the end of its next turn.

Unstoppable (2/Day). Sarevok reduces the damage it takes from an attack to 0.

Sarevok can take 2 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Sarevok regains spent legendary actions at the start of its turn.
Weapon Attack. Sarevok makes a weapon attack.
Command Ally. Saverok targets one ally it can see within 30 feet of it. if the target can see and hear him, the target can make one weapon attack as a reaction and gains advantage on the attack roll.
Frighten Foe (Costs 2 Actions). Sarevok uses his Stunning Gaze attack.