Vaal Hazak

Effluvial Knives. The Vaal Hazak is coated in a gas called effluvium if a target gets hit by anyone of its attacks it will be forced to make a constitution saving throw of 14 if they fail they will fall under the effluvium and will have disadvantage on attack rolls and saving throws. The creature can repeat the saving throw and the beginning of its turn. This lasts at most for two rounds of combat.

Multiattack.  The Vaal Hazak makes two attacks one with its bite and another with its claws.

 Bite. Melee Weapon Attack:  +12 to hit reach 10 ft., one target Hit: 17 (2d10 + 7) piercing damage.

Claw. Melee Weapon Attack: +11 to hit reach 10ft., one target Hit:15 (2d10 +5) slashing damage.

Frightfull Presence. Each creature of the dragons choice within 120 ft. of it must make a DC 17 Wisdom saving throw or become frightened for one minute. A creature can repeat the saving at the end of each its turns, ending the effect on a success for it, the creature is immune to the dragon's Frightfull Presence for the next 24 hours.

Effluvium Coating. The Vaal Hazak almost hollow belly fills up with effluvium increasing its AC from 17 to 19. This last for 2 turns of combat and once it is over it has a recharge of 2 rounds of combat.

Effluvium Ray. During the duration of Effluvium Coating the Vaal Hazak can shoot a blast of effluvium that can go far as 60 ft. and is 10 ft. wide. Each creature in that line must make a DC 17 dexterity saving throw, taking 50 (10d10) force damage on a failed save or half as much on a successful one. Once the attack is done the Effluvium Coating immediately runs out. This attack is also makes the targets under the effects of the effluvium.

The Dragon can take 3 legendary actions, choosing from the actions below. Only one legendary action can be used at a time and only at the end of the creatures turn. The dragon regains spent legendary actions at the start of its turn.

Bite Attack. The dragon makes a bite attack.

Tail Spin. Every creature within 5 ft. of the dragon must make a DC 12 dexterity saving throw or take 13 (2d6 +6) and on a success take half the damage.

Effluvium Slam (Cost 2 Actions). Every creature within 10 ft. of the dragon must succeed a DC 20 dexterity saving throw or take 16 (2d10 + 6) and be under the effects of the effluvium.