Architeuthis

Oath of the Ancients.  Architeuthis has access to the following Oath Spells and can cast each one time per day without using a spell slot.

Spells: [ensnaring strike], [speak with animals], [misty step], [shield of faith]

Necrotic Aura. At the start of each of Architeuthis' turns, each creature within 5 feet of it takes 5 (1d10) cold damage. This aura heals undead within its range. A creature that touches Architeuthis or hits with a melee attack while within 5 feet of him takes 5 (1d10) cold damage.

Great Weapon Fighting. When Architeuthis rolls a 1 or a 2 on a damage die for an attack with his greatsword, while weilding with two hands, can re-roll the die and must take the new roll.

Spellcasting. Architeuthis is a 8th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 14, +6 to hit with spell attacks). Architeuthis has following paladin spells prepared:
1st level (4 slots): [bless], [compelled duel], [heroism], [thunderous smite], [wrathful smite]

2nd level (3 slots): [Branding Smite], [Magic Weapon], [Aid]

Multiattack. Architeuthis makes 2 attacks with his greatsword

Greatsword. Melee Weapon Attack: +7 to hit, reach 10 ft., 1 target. Hit: 10 (2d6 + 3) slashing damage plus 14 (4d6) cold damage.

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

Wrath of the Deep. roiling black tentacles envelop an enemy within 10 feet that he can see. That creature must make a DC15 Strength or Dexterity Saving throw (its choice) or be restrained. While restrained by the tentacles, the creature repeats the saving throw at the end of each of its turns. On a success the creature is free and the tentacles vanish.

Life-Draining Tentacle. Melee Weapon Attack: +7 to hit, reach 15 ft., one target. Hit: 10 (2d6 + 3) necrotic damage. The target must success on a DC 15 CON save or have its hit point maximum reduced by an amount equal to the damage taken. The target dies if this effect reduces its hit point maximum to 0. This reduction lasts until the target finishes a long rest.

Necrotic Ink. (Costs 3 Actions). Architeuthis discharges foul ink in front of himself in a 30-foot cone. Each creature caught in the ink must make a DC 15 CON save, taking 27 (6d8) necrotic damage on a failed save or half as much on a success. A creature that fails its saving throw is blinded until the end of its next turn.