Bond Between Master and Tool. Zhegatl is able to call upon any weapon or person that he has bonded himself with at his will as a bonus action. The round after this is used in Zhegatl still holds the item he called upon then it shatters. 

Ghastly Aura. All creatures within 60ft of Zhegatl instantly become afraid. At the star of every players' turn they must make a DC18 dex saving throw to break free of the frightened effect. At the start of Zhegatl's next turn this effect is reaplied to everything around him. 

Baneful Strike: If a creature is hit by an attack by Zhengatl they must make a DC15 constitution saving throw or they have disadvantage on their next roll against Zhengatl. 

Control of Dominion: At the end of a creature's turn that Zhengatl can see he is able to teleport into an unoccupied space which he can see. Any creature within 20ft of Zhengatl after he teleports takes 2d10 necrotic damage. 

Spellcasting. 

Zhengatl is able to cast these spells and cantrips. He has five spell slots that refill at the end of every three rounds. 

Cantrips: 

Eldritch Blast. 

Ray of Frost 

Shocking Grasp

Spells: 

Eldritch Expulsion. The caster slams their staff into the ground and extends both of their arms outwards. An aura of dark magic appears in a 50ft radius circle around them which reaches 20ft up. All creatures within the aura must make a DC15 wisdom saving throw or take 3d12 necrotic damage and an additional 2d8 force damage. The creature takes half as much on a successful saving throw. 

Eldritch Beam. The caster covers the head of their staff with their offhand and hold the staff above their head. They then mutter the words "I call upon the very darkness around me to be my blade" and remove their hand. A massive pale gray beam is then projected from the staff which goes as far as the user can see and is 10ft wide. Any creature caught within the beam must make a DC15 dex saving throw or take 5d10 necrotic damage on a failed save and half as much on a successful one. 

Blooming Black Nightshade. The caster takes a stomping step forward and shouts the words "the black night blooms once more". The user then bends down on one knee as a black flower appears on their back similar to a deadly nightshade flower. At the end of the next player's turn the flower blooms, releasing a deadly toxic black gas around the user within a 50ft radius lasting a round of combat. After this gas clears the caster rises from the ground once again. All creatures except the caster within this radius must make a DC18 constitution saving throw or take takes 4d12 acid damage. If they succeed the saving throw they only take half the damage +1d10 necrotic damage. Also any attack against the caster done during the duration of this spell has advantage. 

Eldritch Strike. Action Melee Attack. Eldritch Strike: +7 to hit, reach 10 ft., 1 target.  (3d10 + 4) Slashing damage. 

Eldritch Stomp. Action melee attack. Eldritch Stomp: +5 to hit, reach 20ft., all creatures within 20ft of the user. (2d12 +4) necrotic damage. 

Multi-attack. Zhegatl makes three attacks two with Eldritch Strike and one with Eldritch Stomp.  

Enter the description for how legendary actions work for your monster here.

Legendary Action: Eldritch Boom (Costs 2 Actions). Zhegatl removes his helmet revealing his destroyed face. He then spreads his arms and begins to scream. At the start of the second turn after this is casted all creatures within 100ft of him must make a DC20 dex saving throw or take 6d12 necrotic damage and half as much on a successful one. 

Legendary Resistance. Zhegatl has 5 legendary resistances that replenish every 5 turns.