Aspect of Null

Annihilating Aura. Any creature that starts its turn within 30 feet of the aspect must succeed on a DC 25 Constitution saving throw or take 21 (6d6) necrotic damage. Undead are immune to this aura and the aspect may turn it off or on as a bonus action.

Detect Life. The aspect can magically sense the presence of creatures up to 5 miles away that aren’t undead or constructs. It knows the general direction they’re in but not their exact locations. 

Legendary Resistance (5/Day). If the aspect fails a saving throw, it can choose to succeed instead.

Regeneration. The aspect regains 25 hit point at the start of its turn. If the aspect takes radiant damage, this trait doesn’t function at the start of the aspect’s next turn. The aspect’s body is destroyed only if it starts its turn with 0 hit points and doesn’t regenerate.

Turning Immunity. The aspect is immune to features that turn undead.

Unholy Awakening (Recharges after a Short or Long Rest). If the aspect would be reduced to 0 hit points, its current hit point total instead resets to 425 hit points, it recharges its Breath Weapon, and it regains any expended uses of Legendary Resistance.

Unusual Nature. The aspect doesn't require air, food, drink, or sleep. 

Multiattack. The aspect uses Horrifying Visage or Hellfire Orb. It then makes one Bite attack, one Claw attack, and one Tail attack.

Bite. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage plus 13 (2d12) necrotic damage.

Claw. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 19 (2d8 + 10) slashing damage. If the target is a Huge or smaller creature, it is grappled (escape DC 20) and is restrained until this grapple ends. The aspect can have only one creature grappled this way at a time.

Tail. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 26 Strength saving throw or be knocked prone.

Horrifying Visage. Each non-undead creature within 120 feet of the aspect that can see it must succeed on a DC 25 Wisdom saving throw or be frightened for 1 minute. A frightened target can repeat the saving throw at the end of each of its turns, with disadvantage if the aspect is within line of sight, ending the effect on itself on a success. If a target’s saving throw is successful or the effect ends for it, the target is immune to the aspect’s Horrifying Visage for the next 24 hours.

Hellfire Orb. The aspect shoots out a magical ball of fire from its mouth that explodes at a point it can see within 120 feet of it. Each creature in a 20-foot-radius sphere centered on that point must make a DC 25 Dexterity saving throw. The sphere spreads around corners. A creature takes 35 (10d6) fire damage and 35 (10d6) necrotic damage on a failed save, or half as much damage on a successful one.

Breath of Death (Recharge 5–6). The aspect exhales a blast of energy in a 300-foot cone. Each creature in that area must make a DC 26 Dexterity saving throw. On a failed save, the creature takes 78 (12d12) necrotic damage. On a successful save, the creature takes half as much damage. A creature dies if the breath reduces it to 0 hit points. Additionally, any Medium or smaller Humanoid killed by the breath’s damage, as well as every corpse of such a creature within the cone, becomes a wight (see the Monster Manual) under the aspect’s control. The wight acts on the dragon’s initiative but immediately after the dragon’s turn.

The aspect can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The aspect regains spent legendary actions at the start of its turn.

Attack. The aspect makes one Claw or Tail attack.

Wing Attack (Costs 2 Actions). The aspect beats its wings. Each creature within 30 feet of it must succeed on a DC 26 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The aspect can then fly up to half its flying speed.

Ghostly Binding (Costs 3 Actions). The aspect creates ethereal bindings around all creatures of its choice that it can see within 30 feet of it. The targets must succeed on a DC 19 Strength saving throw or be restrained until the end of the aspect’s next turn.

If the aspect’s Unholy Awakening trait has activated in the last hour, it can use the options below as legendary actions.

Summon Undead (Costs 2 Actions). The aspect summons up to five wight in unoccupied spaces within 120 feet of it. They remain until destroyed. Undead summoned in this way roll initiative, act in the next available turn, and obey the aspect. The aspect can have no more than ten Undead summoned by this ability at a time.

Soul Gaze (Costs 3 Actions). The aspect gazes into the souls of all creatures of its choice within a 60-foot cone in front of it. The targets must succeed on a DC 25 Wisdom saving throw or take 39 (6d12) necrotic damage and become frightened until the end of the aspect’s next turn. While frightened in this way, the creature is also paralyzed.