Yelsus, Guardian of Unfettered Chaos

Rejuvenation. If it dies, the naga returns to life in 1d6 days and regains all its hit points. Only a wish spell can prevent this trait from functioning.

Spellcasting. The naga is a 10th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 14, +6 to hit with spell attacks), and it needs only verbal components to cast its spells. It has the following spells prepared:

Cantrips (at will): mage hand, minor illusion, ray of frost

1st level (4 slots): charm person, detect magic, sleep

2nd level (3 slots): detect thoughts, hold person

3rd level (3 slots): lightning bolt, water breathing

4th level (3 slots): blight, dimension door

5th level (2 slots): dominate person

6th level (2 slots): circle of death, harm

8th level (1 slot): power word stun

9th level (1 slot):  meteor swarm

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 7 (1d6 + 4) piercing damage, and the target must make a DC 13 Constitution saving throw, taking 31 (7d8) poison damage on a failed save, or half as much damage on a successful one.

Monstrous Presence. Each creature of Yelsus' choice that is within 120 feet of the Naga and aware of it must succeed on a DC 20 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to Yelsus' Monstrous Presence for the next 24 hours.

Necrotic Eyes (Recharge 5–6). Yelsus' eyes shoot out necrotic beams in a 120-­-foot line that is 10 feet wide. Each creature in that line must make a DC 23 Dexterity saving throw, taking 88 (16d10) necrotic damage on a failed save, or half as much damage on a successful one.