Vaal Hazak

Effluvial Aura: A Vaal Hazak's body produces fungal spores that cause disease and accelerate rot. This aura extends to a 15ft radius from the Vaal Hazak's center. Any creature that starts their turn within, or first enters, this aura must make a Constitution saving throw DC 23 or suffer 3d6 necrotic damage, and become sickened. A successful save renders the creature resistant to the aura for a number of rounds equal to its Con modifier. When enraged, this aura increases to a 20ft radius and +1d6 necrotic damage.

Effluvial Corruption: Anytime a creature takes a cumulative 20 points of necrotic damage they must succeed on a Constitution saving throw or become afflicted with Effluvial Corruption. A creature that is suffering from Effluvial Corruption has their hit point maximum reduced by half and can only benefit from healing at half effectiveness. Accumulated damage is based on damage calculated before resistances and immunities.

Armor of Rotted Flesh: When struck by a melee weapon attack the Vaal Hazak creates a burst of Effluvium. The attacking creature takes 2d6 necrotic damage (no save).

Aversion to Fire: Vaal Hazak is not vulnerable to fire damage, but fire does affect it in unique ways. Whenever Vaal Hazak takes more than 50 points of fire damage in a single round it loses its Effluvial Aura and Armor of Rotted Flesh until it takes a bonus action to restore its Effluvium.

Multiattack: Vaal Hazak can make two claw attacks and a bite attack as an attack action. It can add its tail swipe as a bonus action.

Claw: Melee Weapon Attack: +14 to hit, reach 10 ft., one creature. Hit: 15 (2d6 + 8) slashing damage. When Enraged: +4 (+1d6) necrotic damage.

Bite: Melee Weapon Attack: +14 to hit, reach 15 ft., one creature. Hit: 19 (2d10 + 8) piercing damage. When Enraged: +5 (+1d8) necrotic damage.

Tail Swipe: Melee Weapon Attack: 15ft radius half circle; DC 20 Dex save; Hit: 23 (4d6 + 8) bludgeoning damage.

Effluvium Spray: (Recharge 6); Vaal Hazak gathers Effluvium and fires it as a 120ft line. All targets must succeed on a DC 23 Dexterity save or take 65 (10d12) necrotic damage.

Effluvium Burst: (Recharge 4-6); Vaal Hazak blasts the ground at its feet with Effluvium and creates a toxic cloud around it. Any creature within 60ft must succeed on a DC 23 Con save or take 44 (8d10) necrotic damage and become sickened. Creatures outside 30ft make the save at advantage and do not become sickened on a failure. The cloud lingers and is treated as the Vaal Hazak's Effluvial Aura for 1 minute.

Enrage: Upon being reduced to less than half hit points Vaal Hazak goes into an enraged state. While enraged, its Effluvial Aura increases in size, it deals an extra +1d6 necrotic damage with its claws, and an extra +1d8 necrotic damage with its bite. It also gains the use of its Mythic Action

Vaal Hazak has 3 legendary actions per round.

Tail Sweep: Cost 1 action. Vaal Hazak makes a sweeping attack against all creatures in a 15ft half circle.

Wing Beat: Cost 1 action. Val Hazak flaps its wings in such a way that is causes Effluvium spores to spread about, triggering a Constitution saving throw from all creatures within 30ft. Failure means suffering the effects of the Effluvial Aura.

Take to the Skies: Cost 2 actions. Vaal Hazak flies its full movement without provoking attacks of opportunity.

While enraged, Vaal Hazak had access to a special action that it can use in place of its Legendary Action.

Effluvial Calamity: Cost 3 actions. Vaal Hazak draws in all Effluvial spores that have been spread within 120ft. This negates its aura, extra melee damage, and ends all Effluvial Corruption afflictions. This allows the Vaal Hazak to regain 10d8 hit points and let forth a violent burst of concentrated Effluvium. This is an 80ft burst that requires a DC 23 Con save from all creatures caught. A failed save deals 65 (10d12) necrotic damage and immediate Effluvial Corruption. A successful save takes half and is not corrupted. This also ends the enraged state of the Vaal Hazak.