Brennik Ornstein

Curse of the Mind. (Mythic Trait; Recharges after a Short or Long Rest). When Brennik is reduced to 0 hitpoints, he doesn't die or fall unconscious immediately. Instead, he gains 210 hit points, then erupts in a mound of tentacles. It's size becomes huge, and it's mind blast recharges on a 3-6. It also makes four tentacle attacks as a part of the attack action, as well as use a tentacle attack as a bonus action. It loses access to spellcasting.

Assassinate. During his first turn, Brennik has advantage on attack rolls against any creature that hasn't taken a turn. Any hit Brennik scores against a surprised creature is a critical hit.

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

Psychic Defense. While Brennik is wearing no armor and wielding no shield, his AC includes his Wisdom modifier. Additionally, Brennik always shields his mind. Brennik is immune to magic that allows other creatures to read his thoughts, determine whether he is lying, know his alignment, or know his creature type. Creatures can telepathically communicate with him only if he allows it.

Sense Magic. Brennik senses magic within 120 feet of himself at will. This trait otherwise works like the detect magic spell but isn't itself magical.

Innate Spellcasting (Psionics). Brennik’s innate spellcasting ability is Charisma (spell save DC 21). It can innately cast the following spells, requiring no components:

At will: detect thoughts, levitate, Evard's black tentacles,  scrying

5/day: dominate monster,  power word pain

Legendary Resistance (3/Day). If Brennik fails a saving throw, he can choose to succeed instead.

Multiattack. Brennik makes three Tentacle attacks.

Tentacles. Melee Weapon Attack: +10 to hit, reach 15 ft., one creature. Hit: 30 (4d10 + 8) psychic damage. If the target is Medium or smaller, it is grappled (escape DC 21) and restrained. Only three creatures may be grappled by Brennik in this way at one time.

Mind Blast (Recharge 5–6). Brennik magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 21 Intelligence saving throw or take 10d6 psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Hide.

Spellcasting. Brennik casts a spell with his bonus action from his known spells.

Psychic Shield. Brennik raises a shield against an attack that would hit him. Brennik's AC then goes up by 5 for that attack.

Silvery Barbs.

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

Spellcasting. Brennik casts a spell from his known spells.

Tentacle. Brennik uses a tentacle attack.

Throw. Brennik throws one Large or smaller creature grappled by it. The creature is thrown up to 60 feet in a random direction and knocked prone. The creature takes 1d6 for every ten feet thrown, and if they are thrown at another creature, the other creature must make a DC 18 Dexterity saving throw or be knocked prone and take the same damage.

If Brennik's mythic trait is active, it can use the options below as legendary actions for 1 hour after Curse of the Mind.

Tentacle Eruption (Costs 2 Actions). Brennik erupts in a mass of tentacles, damaging nearby creatures. All creatures within a 15 ft. radius around Brennik must succeed a Dexterity saving throw or take 6d10 + 10 psychic damage, and be grappled. If more than three creatures fail the saving throw, Brennik decides which targets to grapple.