Azernival

Marshal Undead. Unless Azernival is incapacitated, it and undead creatures of its choice within 60 feet of it have advantage on saving throws against features that turn undead.

Limited Magic Immunity. Azernival can’t be affected or detected by spells of 4th level or lower unless it wishes to be. It has advantage on saving throws against all other spells and magical effects.

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

Rejuvenation. If it has a phylactery, a destroyed Azernival gains a new body after using a new host and gathering enough strength, regaining all its hit points and becoming active again. The new body appears within 5 feet of the phylactery.

Regeneration. If Azernival is within his lair at the start of each of his turn's regains 20 HP per turn.

Spellcasting. Azernival is a 19th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 22, +10 to hit with spell attacks). It has the following spells prepared:

1st level (6 slots): Command, Compelled Duel, Searing Smite

2nd level (5 slots): Hold Person, Branding Smite (necrotic Damage)

3rd level (5 slots): Dispel Magic, Blinding Smite (necrotic Damage)

4th level (5 slots): Banishment, Staggering Smite

5th level (4 slots): Destructive Wave (necrotic)

6th level (3 slot): disintegrate, globe of invulnerability

7th level (3 slot): finger of death, Fire Storm, Symbol

8th level (3 slot): dominate monster, power word stun

9th level (2 slot) Psychic Scream, Meteor Swarm

Azernival can innately cast the following spells, requiring no material components:

At will: detect thoughts, disguise self, mage hand, minor illusion

4/day each: charm person, detect magic, invisibility, major image, suggestion

2/day each: dominate person, fly, plane shift, 

Multiattack. Azernival makes three Greatsword attacks.

Greatsword. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 9 (3d8 + 5) slashing damage plus 18 (5d8) necrotic damage.

Hellfire Orb (1/Day). Craven Edge hurls a magical ball of fire 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 18 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.

Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit:9 (3d6 + 2) slashing damage, and the target is cursed if it is a creature. The magical curse takes effect whenever the target takes a short or long rest, filling the target’s thoughts with horrible images and dreams. The cursed target gains no benefit from finishing a short or long rest. The curse lasts until it is lifted by a remove curse spell or similar magic.

Parry. Azernival adds 6 to its AC against one melee target that would hit it. To do so, Azernival must see the attacker and be wielding a melee weapon. Plus 6 AC last's until end of parry target's turn.

Azernival can take 5 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. Azernival regains spent legendary actions at the start of its turn.

Summon Ghoul. (cost 1 Action). Azernival reach's to the plane of the dead and summon's 1D6 Ghoul's to battle until slain

Multiattack. (Costs 2 Actions). Azernival makes two Greatsword attacks.

 Frightening Gaze (Costs 2 Actions). Azernival fixes its gaze on one creature it can see within 10 feet of it. The target must succeed on a DC 20 Wisdom saving throw against this magic or become frightened for 1 minute. The frightened target can repeat the saving throw at the end of each of its turns, 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 Azernival's gaze for the next 24 hours.

Disrupt Life (Costs 3 Actions). Each living creature within 20 feet of Azernival must make a DC 20 Constitution saving throw against this magic, taking 21 (6d8) necrotic damage on a failed save, or half as much damage on a successful one.

Sacrifice Ghoul. (3/day.) (Costs 5 Actions). If Azernival is within his lair he can sacrifice summoned ghouls up to a range of 30 feet from him. to regain strength and will regain 20 HP X the amount of ghouls sacrificed up to a limit of 15 ghouls per use.