Avatar of Hadar

Frightful Presence - When a creatures first enters into battle with Hadars avatar, they must make a Wisdom save (DC 25) otherwise be frightened until the next dawn. A creature may reroll their save at the end of each of their turns.

Spellcasting. The Avatar of Hadar has innate spellcasting.

He can cast Eldritch Blast;at will.

He can cast Hunger of Hadar at 6th level 6 times per day.

He can cast Arms of Hadar at 5th level 8 times per day.

He can cast Banishment at 8th level 4 times per day.

Hadar makes 4 attacks.

Tentacle Attack - Melee Weapon Attack: +17 to hit, reach 20 ft, 1 target. Hit (2d8 bludgeoning and 2d10 psychic damage.) 

Claw Attack - Melee Weapon Attack: +17 to hit, reach 20ft, 1 target. Hit (3d8 slashing damage and 2d12 force damage)

Grapple - Upon hitting with a melee attack Hadar attempts to grapple an enemy (STR dc of 25). If grappled he can use one of his attack actions to squeeze you, which must contest with another STR save (DC 25) otherwise take 5d10 bludgeoning damage.

Acid Breath - Range 50ft cone. Hadar spits up a vile acidic substance. All creatures within the cone must make a Dex save (DC 23) otherwise take 10d8 acid damage. On a successful save creatures take half as much.

Psychic Blast - Range 200 feet. On his turn Hadar may choose to forgo any attacks and do a mind piercing scream. All creatures must make an intelligence save of 26 otherwise take 10d10 psychic damage or half as much on a successful save. If any target fails they must then make a constitution save or be stunned until the end of their next turn. (Recharge on a d6 5-6 roll)

Intellect Devour - Range 150 feet. On his turn Hadar may choose any creature he can see within range and attempt to drain their intellect. The target must succeed a INT saving throw (DC 22) otherwise take 8d10 psychic damage, half on a successful save. If the target fails, they lose 1d6-2 Intelligence. This can only be restored by the means of a greater restoration spell. (Regain on a roll of 12 on a d12)

Eldritch Push - Range 50 feet. On his turn Hadar may use an overwhelming amount of force to push away all creatures near him. Any creature within the affected area must make a STR saving throw (DC 24) otherwise be pushed away 60 feet. On a failed save creatures also take 10d6 force damage. On a successful save creatures take half as much and are not pushed back.

Teleport - As a bonus action Hadar can choose to teleport to an unoccupied space that he sees within 60 feet of him.

Eldritch Might - When Hadar is targeted by a spell of either 3rd level or lower, he can decide to negate the spell entirely 6 times per day.

Hadar gains 6 legendary actions per day.

Legendary Resistance (1 legendary action) - On a failed saved Hadar can otherwise choose to save instead.

Regenerate (3 legendary actions) - When Hadar hits a threshold of damage, he may choose to regenerate his health. He regains 300 hit points.

Hadar has 1 mythic action per year.

Reborn - When Hadar falls for the first time he can choose to regain all of his missing HP. Thus in doing so his avatar becomes slightly weaker, lowering his ac by 2.