Vaelzaryn, The Violet Drowned King

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

Shadow Fey Changeling. Vaelzaryn can use an action to polymorph into any Medium or small humanoid he has seen, or back into his true form. His statistics remain the same.

Aura of the Unknown Deep. Each enemy of Vaelzaryn’s choice that starts its turn within 30 feet must succeed on a DC 23 Wisdom saving throw or be frightened until the start of its next turn. If a creature fails this save by 5 or more, it is also stunned until the end of its turn.

Spinosaurus Dread Mantle. Vaelzaryn’s shadow-sail (spine crest) radiates void energy. Once per turn when Vaelzaryn hits with an Ulak, the target takes an extra 27 (6d8) psychic damage.

Eldritch Predator. Vaelzaryn can make opportunity attacks with spells and weapon attacks. When he reduces a creature to 0 hit points, he regains 30 hit points.

Innate Spellcasting / Warlock Spellcasting. Vaelzaryn is a 20th-level spellcaster. His spellcasting ability is Charisma (spell save DC 23, +15 to hit with spell attacks).

He requires no material components.

At Will: eldritch blast (4 beams), detect magic, disguise self, darkness, misty step
3/Day Each: blight, hunger of hadar, Wrathful smite, banishment, synaptic static
2/Day Each: finger of death, shadow of moil, negative energy flood, feeblemind
1/Day Each: power word pain, maddening darkness, psychic scream

Multiattack. Vaelzaryn makes three Ulak of the Drowned King attacks or casts one spell and makes two Ulak attacks.

Ulak of the Drowned King. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 19 (2d10 + 6) slashing damage plus 22 (5d8) necrotic or psychic damage (Vaelzaryn’s choice).

Eldritch Devour (Recharge 5–6). Vaelzaryn releases a cone of void-tinged energy in a 60-foot cone. Each creature in the area must make a DC 23 Constitution saving throw, taking 72 (16d8) necrotic and psychic damage on a failed save, or half as much on a successful one. Creatures reduced to 0 hit points by this effect disintegrate into shadow.

Spinosaurus Shadow Manifestation (1/Day). Vaelzaryn summons a colossal spectral spinosaurus avatar in a 40-foot radius centered on himself for 1 minute. Enemies in the area have disadvantage on saving throws and take 15 psychic damage at the start of each of their turns. Vaelzaryn gains advantage on all attack rolls while this effect lasts.

Shadow Slip. Vaelzaryn teleports up to 60 feet to a space he can see in a burst of purple-black shadow.

Hex of the Deep. Vaelzaryn curses one creature he can see within 90 feet. For 1 minute, the target has disadvantage on saving throws against Vaelzaryn’s spells and takes an extra 14 (4d6) necrotic damage whenever Vaelzaryn hits it.

Void Counter. When a creature Vaelzaryn can see casts a spell within 60 feet, Vaelzaryn can attempt to counter it as if casting counterspell at 8th level.

Vaelzaryn 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. Vaelzaryn regains spent legendary actions at the start of his turn.

Ulak Strike. Vaelzaryn makes one Ulak of the Drowned King attack.

Cantrip. Vaelzaryn casts eldritch blast.

Shadow Warp (Costs 2 Actions). Vaelzaryn teleports up to 60 feet and becomes invisible until the start of his next turn.