Chaos

Chaos Form. The elemental ignores movement restrictions caused by the elements. At the start of each of its turns, each creature within 5 feet of it takes 3 (1d6) fire damage plus 3 (1d6) acid damage, 3 (1d6) cold damage, 3 (1d6) lightning damage, and 3 (1d6) thunder damage. A creature also takes this damage when it touches the elemental or hits it with a melee attack while within 5 feet of it.

Fiendish Hybrid. The elemental is also a fiend (demon).

Legendary Resistance (3/Day). If the elemental fails a saving throw, it can choose to succeed instead.

Siege Monster. The elemental deals double damage to objects and structures.

Magic Resistance. The elemental has advantage on saving throws against spells and other magical effects.

Magic Weapons. The elemental's weapon attacks are magical. end of the target's next turn.

Multiattack. The elemental makes four attacks: a fling, a scorch, a slam, and a smash attack

Fling. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage plus 4 (1d8) thunder damage, and the target must succeed on a DC 20 Constitution saving throw or be pushed 30 feet in a direction of the elemental's choice and deafened until the  Unsecured objects of size Huge or smaller are pushed automatically.

Scorch. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 22 (5d8) fire damage, and if the target is a creature or a flammable object, it ignites. Until a creature takes an action to douse the fire, the target takes 11 (2d10) fire damage at the start of each of its turns.

Slam. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage plus 4 (1d8) cold damage, and the target is grabbed by the water arm (escape DC 20) and restrained while it is grabbed.

Smash. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 21 (3d8 + 8) bludgeoning damage, and the target must succeed on a DC 20 Strength saving throw or be knocked prone.

Transmute (Recharge 5-6). The elemental alters the form of each creature and object within 30 feet of it to confuse the elements. Ground, water, and air in the area is transformed to slurry: heavily obscured water that is difficult terrain. Each other creature and object in the area must make a DC 20 Constitution saving throw. On a failed save, a target takes 39 (6d12) force damage and is stunned until the end of its next turn. On a success, it takes half damage and isn't stunned.

Destructive Wrath. The elemental two melee attacks using different weapons. The attacks must be made against objects or structures.

Howl of Terror (Costs 2 Actions). The elemental roars with primordial fury that resonates in the soul. Each creature of the elemental's choice that is within 120 feet of the elemental must make a DC 20 Wisdom saving throw. On a failed save, a creature is frightened until the end of its next turn. On a success, a creature becomes immune to the elemental's Howl of Terror for the next 24 hours.

Primordial Flow (Costs 2 Actions). The elemental moves its speed without provoking opportunity attacks. For this move, it can enter a hostile creature's space and it can move through a space as narrow as 1 inch wide without squeezing, but it can't end the movement in such a place. The first time it enters a creature's space during this movement, the creature takes damage from the elemental's Chaos Form trait.