Avatar of the Clockwork Primordial

Immutable Form. The Avatar is immune to any spell or effect that would alter its form.

Unusual Nature. The Avatar doesn’t require air, food, drink, or sleep.

Magical Weapons. Melee attacks made by this creature are magical.

Clockwork Construct. Any character fighting the Avatar can see that the complex arrangement of its workings gives it a unique vulnerability. Any character within 5 feet of the construct can use an action to attempt a DC 21 Dexterity check using jeweler’s tools or thieves’ tools. On a success, the Avatar takes 15 bludgeoning damage as it components start to grind, and it is no longer able to recharge its Primordial Corruption.

Chaotic Forme. The Aberrant design of this creature affects the minds of those that see it. At the beginning of each round, all non-construct creatures within 180 feet that can see this creature must succeed on a DC 19 Wisdom Saving throw or be frightened of the Avatar for three rounds. If a creature succeeds on the saving throw, they do not need to roll again during this combat. If a creature fails more than three times, they must roll on the short-term madness chart. If they fail the saving throw six times, they must roll again on the short-term madness chart and once on the long-term madness chart. If they fail nine times, they must roll on the Long-term madness chart again and roll for an Indefinite madness. 

Multiattack. The Avatarmakes three tentacle attacks, each of which it can replace with one use of Fling.

Tentacle. Melee Weapon Attack: +17 to hit, reach 30 ft., one target. Hit: 20 (3d6 + 10) bludgeoning damage, and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained. The Avatar has 5 tentacles, each of which can grapple one target.

Fling. One Large or smaller object held or creature grappled by the Avatar is thrown up to 60 feet in a random direction and knocked prone. If a thrown target strikes a solid surface, the target takes 3 (1d6) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a DC 18 Dexterity saving throw or take the same damage and be knocked prone.

Bladed Wings. Melee or Ranged Weapon Attack: +11 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 19 (2d8 + 10) slashing damage.

Primordial Corruption (Recharge 5–6). The Avatar exhales a blast of lightning and twisted magic in a 90-foot cone. Each creature in that area must make a DC 22 Dexterity saving throw, gaining no benefit from cover (other than total cover) and taking 38 (7d10) lightning damage and 38 (7d10) force damage on a failed save, or half as much damage on a successful one.

The Avatar 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. The Avatar regains spent legendary actions at the start of its turn.

Tentacle Attack or Fling. The Avatar makes one tentacle attack or uses its Fling.

Dimensional Teleport (Costs 2 Actions). The Avatar teleports up to 60 ft away taking anything it has grappled with it.

Primordial Blast (Costs 3 Actions). Once per combat when this creature is below half health, this creature overcharges its core. At the start of its next turn after taking this legendary action, it erupts in an explosion of twisted magic. Creatures within 60 ft. must make a DC 17 Dexterity saving throw, being dealt 55 (10d10) force damage on a fail, and half as much on a success. Then, magic inside of the circle stops functioning as expected. For 3 turns, spells cannot be cast while within this area, nor can any creature in this area be targeted by magic. The Avatar cannot use its Primordial Corruption Attack for three weeks after using this action.