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.
Incorporeal. The naga is immune to bludgeoning, piercing, and slashing damage.
Spellcasting. The naga is a 20th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 20, +12 to hit with spell attacks), and it needs only verbal components to cast its spells. It has the following spells prepared:
1st level (4 slots): shield, magic missile
2nd level (3 slots): detect thoughts, invisibility
3rd level (3 slots): dispel magic
4th level (3 slots): blight, sickening radiance
5th level (3 slots): cloudkill, scrying
6th level (3 slots): chain lightning, mental prison
7th level (2 slots): finger of death, power word pain
8th level (1 slot): power word stun, feeblemind
9th level (1 slot): psychic scream
Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one creature. Hit: 32 (8d8) poison damage, and the target must make a DC 20 Constitution saving throw, becoming poisoned on a failed save.
Constrict. Melee Weapon Attack: +12 to hit, reach 10 ft., one creature. Hit: target takes 24 (4d12) psychic damage, and becomes psychically entangled by the naga. While entangled in this way, they take 4d12 damage at the start of the naga's turn. If a target moves while entangled, they take 1d12 psychic damage for each 5 feet of movement, up to a maximum of 6d12 damage per turn. If the creature is ever more than 30 feet away from the point at which they became entangled, the entanglement ends.