Transgress the Mind. When a creature casts a spell requiring concentration at Zhulodok, it sends visions through this connection.

Until the caster loses concentration, at the start of each of Zhulodok's turns, each creature within 20 feet of the caster, including the caster, must make a DC 23 Intelligence saving throw, taking 100 (18d10) psychic damage on a failed save, or half as much on a successful one. The caster has disadvantage on the save.

Not of this World. Zhulodok has advantage on saving throws against spells and other magical effects.

Scour from Existance. When Zhulodok reduces a creature to 0 hit points, that creature's body becomes a pile of white dust. The creature can be restored to life only by means of a true resurrection or a wish spell.

Multiattack. Zhulodok can use its Titan's Presence. It then makes six attacks: four with its fists, and two with its tentacles.

Fist. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 27 (4d8 + 9) bludgeoning damage. If the attack hits, the target is grappled (escape DC 23) if it is a Huge or smaller creature and Ulamog doesn't have four other creatures grappled. Until this grapple ends, the target is restrained and takes 22 (4d10) psychic damage at the start of each of its turns.

Tentacle. Melee Weapon Attack: +17 to hit, range 30 ft., one target. Hit: 23 (4d6 + 9) bludgeoning damage. If the target is a creature, it must succeed on a DC 23 Strength saving throw of be knocked prone. 

Titan's Presence. Each creature of Zhulodok's choice that is within 240 feet of Zhulodok and aware of it must succeed on a DC 20 Inteligence saving throw or become frightened for 1 minute and rolls a d8 to determine what it does during its turn. On a 1 to 2, the creature does nothing. On a 3 or 4, the creature is afflicted with short-term madness. On a 5 or 6, the creature takes no action or bonus action and uses all its movement to move in a randomly determined direction. On a 7 or 8, the creature makes a melee attack against a randomly determined creature within its reach or does nothing if it can’t make such an attack. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to Zhulodok's Titan Presence for the next 24 hours.

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

Attack. Zhulodok moves up to 30 feet and makes a fist attack.  

Blight Herder (Costs 2 Actions). Zhulodok alters the nature of all things in a 30-foot-radius sphere centered on a point within 120 feet of it. Each creature in that area must make a DC 23 Dexterity saving throw, taking 55 (10d10) psychic damage on a failed save, or half as much on a successful one. For each creature that fails the saving throw, an Eldrazi Scion appears in an unoccupied space within 5 feet of that creature. The Eldrazi Scion act right after Zhulodok on the same initiative count, gaining a +7 bonus to their attack and damage rolls, and fighting until they are destroyed. They disappear when Zhulodok dies. 

All is Dust (Costs 3 Actions). Zhulodok consumes the mana of everything in a 90-foot cone. Each  creature in that cone must make a DC 27 Constitution saving throw, taking 60 (17d6) force damage + 30 necrotic damage on a failed save, or half as much on a successful one. The creatures hit point maximum is reduced by an amount equal to the necrotic damage, and Zhulodok regains that amount per creature. A creature becomes a pile of white dust if this damage leaves it with 0 hit points. The area becomes difficult terrain.