Aura of Void. Every creature within 10 ft. is dealt 4 necrotic damage.

Legendary Resistance(3/day). If Grey fails a saving throw it can choose to succeed instead.

The Endless Void. When Grey is below 130 hit points, it regains 14 hit points every time it ends its turn.

Multiattack. Grey makes 6 claw attacks.

Claw. Melee Weapon Attack: +14 to hit, reach 10 ft., 1 target. Hit: 18 (2d8 + 10) necrotic  damage. 

Radiation Ray. RangedWeapon Attack: +10 to hit, range 80/360 ft., 3 target. Hit: 15 (3d10)  radiant damage.

Grey 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. Grey regains spent legendary actions at the start of its turn.

Necrotic Storm(Costs 2 Actions). Grey releases a storm of necrotic needles. Each creature within 20 ft. must make a DC 19 dexterity saving throw. On a failure,  they take 15 (3d10) necrotic or on a success half of that.

Fury of the Void.Grey makes 3 claw attacks.

Void Teleportation. Grey makes a small void jump. It teleports up to 80 ft. then makes a claw attack.

A-VOID-ence(Costs 2 Actions). Grey shifts into the void making it hard to hit. Attacks against it have disadvantage and creatures that it with an attack are dealt 6(2d6) necrotic damage until the beginning of its  turn.