Legendary Resistance (3/day). If Zalazaar fails a saving throw, he can instead choose to succeed.

Dark Inspiration (1/day). Zalazaar can spend 4 hours in contemplation with his patron master and at the end of this meditative trance he gains a point of inspiration that he can use at any point during the day, opting to give himself advantage on a roll of his choice or force disadvantage on a hostile creature’s roll of his choice. Once this ability has been used he must wait until the following day to use it again, undergoing another 4 hour trance. The inspiration can manifest as a set of small horns, glowing eyes or spikes sprouting from under his skin, giving him a fiendish look.

Magic Resistance. Zalazaar has advantage on saving throws against spells and other magical effects.

Dark One's Blessing. Zalazaar gains 10 temporary hit points when he reduces a creature to 0 hp, he also gains this bonus when another creature reduces a creature to 0 hp within 40 ft. of him, these temporary hit points do not stack. At the beginning of his turn, if he is not Incapacitated or took more than 50 points of damage in one turn he regains 25 (3d8 + 9) hit points. 

Pin of Shielding. Zalazaar wears a pin wherever he goes, shaped like a jagged set of jaws. It is a gift from his master that provides a continuous shield around him. This shield gives him a +5 to his AC and anyone who attempts to remove it physically from his person must succeed a DC 16 Constitution saving throw or take 18 (6d6) force damage and be knocked backwards 10ft and prone, taking half damage and not being knocked backwards on a successful save. The pin has an AC of 8 and has 15 hit points, though all attacks made against it are made with disadvantage. Removing this pin from his person or destroying it deprives him of the +5 bonus to his AC.

Stolen Knowledge. Zalazaar possesses a scroll for the spell Teleport that can be cast at level 7. If he uses this spell, he must spend 3 weeks to search and replace the spell scroll. 

Multiattack. Zalazaar makes three Arcane Burst attacks.

Arcane Burst. Melee or Ranged Spell Attack: +9 to hit, reach 5 ft. or range 120 ft., one target. Hit: 20 (3d10 + 5) force damage.

Force Blast. Each creature in a 20-foot cube originating from the abjurer must make a DC 16 Constitution saving throw. On a failed save, a creature takes 32 (8d8) force damage and is pushed up to 10 feet away from the abjurer. On a successful save, a creature takes half as much damage and isn’t pushed.

Spellcasting. Zalazaar casts one of the following spells, using Intelligence as the spellcasting ability (spell save DC 16, +9 to hit):

At will: dancing lights, mage hand, message, prestidigitation

2/day each: dispel magic, lightning bolt, mage armor, fireball

1/day each: arcane lock, banishment, globe of invulnerability, invisibility, wall of force

Zalazaar has 4 pact slots, which replenish daily after a long rest. He can spend them to cast the following Warlock spells:

At will: burning hands, blade ward

2/day: counterspell, hellish rebuke

1/day: fireball, wall of fire

Arcane Ward (Recharge 4–6). When Zalazaar or a creature it can see within 30 feet of it takes damage, Zalazaar magically creates a protective barrier around himself or the other creature. The barrier reduces the damage to the protected creature by 20 (3d10 + 5), to a minimum of 0, and then vanishes.

Zalazaar 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. Zalazaar regains all used legendary actions at the start of his turn.

Arcane Burst. Zalazaar makes an attack using his Arcane Burst.

Cantrip. Zalazaar can cast any cantrip spells he has prepared.

Spellcasting (2 Actions). Zalazaar can cast a spell that he has prepared.

Warding Pulse (2 Actions). Zalazaar creates a pulse of energy centred around himself in a 15ft radius. All creatures caught in this radius must make a DC 16 Strength saving throw or be thrown 30ft backwards and take 9 (3d6) force damage, not getting pushed backwards and taking only half damage on a successful save.

Wrathful Burst (3 Actions). Zalazaar uses his Multiattack for Arcane Burst.