Astrazel

Legendary Resistance (3/Day). If the skull lord fails a saving throw, it can choose to succeed instead.

Master of the Grave. While within 30 feet of the skull lord, any undead ally of the skull lord makes saving throws with advantage, and that ally regains 1d6 hit points whenever it starts its turn there.

Evasion. If the skull lord is subjected to an effect that allows it to make a Dexterity saving throw to take only half the damage, the skull lord instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Reconstruction. When Astrazel is reduced to 0 hit points, its body breaks into seven pieces: two arms, two legs, a tail, a torso, and a head. Each piece is a small object with AC 29, 30 hit points, and immunity to psychic and poison damage. After 1d6 days, if all pieces are still within 6 miles of each other, they all teleport to the location of the head piece and merge with it, whereupon Astrazel regains all its hit points and becomes active again.

Spellcasting. Astrazel is a 13th-level spellcaster. Its spellcasting ability is Charisma (spell save DC18, +10 to hit with spell attacks). Astrazel knows the following sorcerer spells:

Cantrips (at will): chill touch, fire bolt, mage hand, poison spray, ray of frost, shocking grasp, eldritch blast

1st level (4 slots): magic missile, expeditious retreat, thunderwave

2nd level (3 slots): mirror image, scorching ray

3rd level (3 slots): fear, haste, animate dead

4th level (3 slots): dimension door, ice storm

5th level (2 slots): cloudkill, cone of cold

6th level (1 slot): eyebite

7th level (1 slot): finger of death

Dust Form: As long as Astrazel's Head is intact it can disperse its essence to the wind

Multiattack. Astrazel makes three bone staff attacks.

Bone Axe. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 4) slashing damage plus 14 (4d6) necrotic damage.

The skull lord can take 4 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 skull lord regains spent legendary actions at the start of its turn.

Bone Staff (Costs 1 Actions). The skull lord makes a bone staff attack.

Cantrip. The skull lord casts a cantrip.

Move. The skull lord moves up to its speed without provoking opportunity attacks.

Summon Undead (Costs 2 Actions). Up to five skeletons or zombies appear in unoccupied spaces within 30 feet of the skull lord and remain until destroyed. Undead summoned in this way roll initiative and act in the next available turn. The skull lord can have up to 10 undead summoned by this ability at a time.