Teleport. As a free action Zeroa The God of the void can teleport up to 120 feet in adition to their walking speed

Reflecting Mist Any time the Zeroa The God of the void is targeted by a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d12. On a 1 to 11, Zeroa The God of the void is unaffected. On a 12, the Zeroa The God of the void is affected, and the effect is reflected back at the caster as though it originated from Zeroa The God of the void, turning the caster into the target. Zeroa is also immune to any spell of 6th level or lower. Zeroa's resistances and immunities can not be bypassed by any means.

Uneasy existence: when forced to make a Dexterity or Constitution saving throw Zeroa takes half damage and no damage on a successful. 

Regeneration: Zeroa regains 10 hp per round and if they did not take any damage during the round they heal an extra 40 hp

Spellcasting. Zeroa The God of the void is a 30th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 24, +20 to hit with spell attacks). Zeroa The God has following wizard spells prepared: 
1st level (5 slots): shield, absorb elements, searing smite

2nd level (4 slots): darkness

2/round counterspell or dispel magic

4rth level (4 slots) shadow of the moil (no concentration)

5th level (3 slots) destructive wave, cone of cold

6th level (2 slots) Blade barrier, chain lightning, disintegrate, heal

7th level (2 slot) regenerate, prismatic spray, power word pain

8th level (1 slot) Power word stun, feeblemind, Abi-Dalzim’s Horrid Wilting, anti-magic field 

9th level (1 slot) psychic screech , power word heal

Legendary resistance:

Zeroa gets 5 legendary resistances per day, when Zeroa uses a legendary resistance it can choose to succeed saving throw.

Multi-attack. Zeroa The God of the void makes 5 attacks per turn

Blade of Transmutation. Melee Weapon Attack: +22 to hit, reach 10 ft., 1 target. Hit: 66 2 times (2d10 +2d8+25) [force or psychic] damage. 

Bow of Transmutation. Ranged Weapon Attack: +20 to hit, range 120/300 ft., 2 targets. Hit: # (2d12+3d8+ 30) [force or psychic] damage.

As a bonus action Zeroa The God of the void can change the form of her weapon of transmutation into a Blade or a Bow.

Agile Pary. once per round Zeroa The God of the void can add its proficiency bonus to its AC for one attack

The Zeroa The God of the void can take 7 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 Zeroa The God of the void regains spent legendary actions at the start of its turn.

Attack Zeroa The god of the void makes a bow or sword attack.

Retribution (Costs 3 Actions recharge 5-6). All the damage that Zeroa The God of the void is ignored until then end of Zeroa The  God of the void's turn at which point it takes an action, bonus action and reaction the shoot a beam of retribution at everyone who did damage to it during that turn. all creatures hit by the beam first roll 1d6 then take damage equal to the amount they did to Zeroa The God of the void while the retribution was active or twice as much if they rolled a 5 or 6.

Mist Lash (Costs 2 Actions)  Zeroa The God of the void can form a spectral weapon and slashes 2 35ft cones with it all creatures in that area have to make a DC 28 dex save or take 5d12 force + 50 psychic damage and is stunned and restrained until the end of its next turn

Consume Zeroa The God of the void can attempt to consume a creature that has less than a half of its hp remaining. Zeroa The God of the void makes a special roll contested by the targets con or dex save. Zeroa The God of the void makes the roll with a + 19 to the roll if the target rolls lower than Zeroa The God of the void's roll then it is consumed by it as tendrils on mist drag it into the god's body where it is kept until it is knocked unconscious. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the Zeroa The God of the void, and it takes 120 (20d10) force damage at the start of each of the Zeroa The God of the void's turns, this damage ignores resistance and immunity.

If the Zeroa The God of the void takes 100 damage or more on a single turn from a creature inside it, the Zeroa The God of the void must succeed on a DC 25 Constitution saving throw at the end of that turn or expel all consumed creatures from itself, which fall prone in a space within 10 feet of the Zeroa The God of the void. If Zeroa The God of the void is banished it leaves all consumed creatures behind.

if a creature dies while consumed by Zeroa The God of the void it becomes part of the god and the god gains hp equal to twice the characters level

2nd phase (Costs 1 Action). When Zeroa The God of the void is reduced to half health gains 120 hp, 120 max hp, consume and mist lash. 

That Wasn't Even My Final Form (Costs 1 Action) When Zeroa The God of the void reaches 0 hp it comes back with 240 hp and loses all actions but gains the ability to shoot giant lasers as an attack. It makes four laser attacks and each laser forces each creature in a 100 ft line to make a dex save or take DC 15d10 + 10 damage on a successful save the creature takes 1/4th damage this is not affected by evasion or similar effects.