Actions

Multiattack. Setareh can use her Frightful Presence. She then makes three attacks: one with his Bite and two with his Claws.

Bite. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 2d10+9 20 (2d10 + 9) piercing damage plus 14 (4d6) necrotic damage.

Claw. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 2d6+9 16 (2d6 + 9) slashing damage.

Tail. Melee Weapon Attack: +16 to hit, reach 20 ft., one target. Hit: 2d8+9 18 (2d8 + 9) bludgeoning damage. If the target is a creature, it must succeed on a DC 24 Strength saving throw or be knocked prone.

Frightful Presence. Each creature of Setareh's choice that is within 120 feet of him and aware of him must succeed on a DC 22 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if Anecralon is within line of sight, ending the effect on itself on a success.

Necrotic Breath (Recharge 5–6). Anecralon exhales necrotic energy in a 90-foot cone. Each creature in that area must make a DC 24 Constitution saving throw, taking 16d10 88 (16d10) necrotic damage on a failed save, or half as much damage on a successful one.

Legendary Actions

Setareh 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. Setareh regains spent legendary actions at the start of her turn.

Detect. Setareh makes a Wisdom (Perception) check.

Tail Attack. Anecralon makes a Tail attack.

Wing Attack (Costs 2 Actions). Setareh beats her wings. Each creature within 15 feet of her must succeed on a DC 24 Dexterity saving throw or take 18 3d6+8 (3d6 + 8) bludgeoning damage and be knocked prone. Setareh can then fly up to half his flying speed.

If Setareh's Cosmic Rebirth trait has activated in the last hour, she can use the options below as legendary actions.

Cosmic Nova (Costs 2 Actions). Setareh releases a burst of astral energy in a 30-foot radius. Each creature in that area must make a DC 22 Dexterity saving throw, taking roll:4d8 18 (4d8) force damage on a failed save, or half as much damage on a successful one. Hit points lost in this manner can only be regained by finishing a short or long rest.

Void Collapse (Costs 2 Actions). Setareh causes a point she can see within 100 feet of her to implode with void energy, creating a gravitational pull. Each creature within 20 feet of the point must succeed on a DC 22 Strength saving throw or be pulled toward the centre, becoming restrained until the start of Anecralon's next turn. A restrained creature must succeed on a DC 22 Constitution saving throw at the start of its next turn or take roll:6d6 21 (6d6) necrotic damage as the void energy is compressed around it.

Lair Actions

On initiative count 20 (losing initiative ties), Setareh takes a lair action to cause one of the following effects; Setareh can’t use the same effect two rounds in a row:

Astral Eclipse. Cosmic darkness snuffs out all light in the lair. Spells of 7th level or lower that create light are dispelled. A hostile creature in the lair with darkvision must succeed on a DC 22 Wisdom saving throw or be cursed for 1 minute, losing its darkvision for the duration.

Astral Veil. Setareh summons a 40-foot-radius sphere of dense astral mist. The area is heavily obscured. Hostile creatures in the mist have disadvantage on attack rolls and Wisdom (Perception) checks relying on sight. A creature that enters the area for the first time on a turn or starts its turn there must succeed on a DC 22 Intelligence saving throw or take 14 (4d6) psychic damage and have its speed reduced by 10 feet until the end of Setareh's next turn.

Void Surge. Setareh conjures a 20-foot-radius vortex of swirling void energy centred on a point within 120 feet of her. The vortex lasts until Setareh uses another lair action. A creature that enters the area for the first time on a turn or starts its turn there must succeed on a DC 22 Strength saving throw or be pulled to the nearest unoccupied space to the centre of the vortex and restrained for the duration. A restrained creature can use its action to repeat the saving throw, ending the effect on itself on a success.

Regional Effects

Setareh exerts a corrupted influence on the surrounding region, manifesting in distinct magical phenomena:

Cosmic Flux. Within 2 miles of the Athenaeum, the stability of magic is compromised. While in this area, there is a 10 percent chance spellcasters must succeed on a DC 18 spellcasting ability saving throw or trigger a wild magic surge when casting a spell.

Dreams of the Void. Within 5 miles of the Athenaeum, the emptiness of the Void seeps into the dreams of sleeping creatures. These dreams are filled with visions of endless libraries and boundless corridors, sparking a deep yearning for forbidden knowledge. Anyone who sleeps in this area for at least 1 hour must succeed on a DC 18 Wisdom saving throw or suffer one level of exhaustion after waking.

Phantom Fragments. Fragments of realities that have been consumed by the Athenaeum manifest physically as shimmering motes that coalesce into brief, vivid reenactments of past events or forgotten knowledge. A creature observing these manifestations must make a DC 18 Intelligence saving throw to avoid being overwhelmed by the influx of information. On a failure, the creature suffers a short-term madness effect as its mind is overwhelmed by the visions.

Upon Setareh's defeat, these effects begin to fade, dissipating completely over the course of 1d10 5 (1d10) days.