Avatar of Leviathan, Goddess of the Sea and Mother of Monsters

Legendary Resistance (6/Day). If the leviathan fails a saving throw, she can choose to succeed instead.

Mother of Monsters. The Avatar can summon forth creatures of the deep to serve her. As a bonus action, she can summon 1d4 Water Elementals, 1 Kraken, or 2d6 Merrow within 90 ft. These creatures obey her commands and remain for 1 hour or until dismissed or destroyed.

Oceanic Majesty. Creatures within 60 feet of the Avatar must make a DC 24 Wisdom saving throw at the start of their turn or be frightened for 1 minute. Creatures failing the save by 5 or more are also paralyzed while frightened. A creature can repeat the saving throw at the end of each of their turns, ending the effect on a success.

Formless Tide. The Avatar can move through spaces as narrow as 1 inch wide without squeezing. Any creature she moves through must succeed on a DC 25 Strength saving throw or be knocked prone and pushed 20 ft. away.

Oceanic Awakening (Recharges after a Short or Long Rest). If Leviathan would be reduced to 0 hit points, her current hit point total instead resets to 425 hit points, it recharges its Call of the Abyss, and she regains any expended uses of Legendary Resistance. Additionally, Leviathan can now use the options in the “Mythic Actions” section for 1 hour. Award a party an additional 105,000 XP (210,000 XP total) for defeating her after her Oceanic Awakening activates.

Multiattack. The Avatar can make three attacks per turn: two with her Trident of Abyss and one with her Tail.

Trident of Abyss. Melee Weapon Attack: +18 to hit, reach 20 ft., one target. Hit: 40 (5d10 + 14) piercing damage. The target must make a DC 26 Constitution saving throw or be suffused with abyssal energy, taking 30 (6d10) necrotic damage at the start of its next turn.

Tail. Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 35 (4d12 + 14) bludgeoning damage. The target must succeed on a DC 25 Strength saving throw or be grappled (escape DC 25). The Avatar can grapple up to 2 creatures at once with her tail.

Drown Soul. The Avatar targets one creature within 150 ft. of her. The target must make a DC 27 Wisdom saving throw or be mentally submerged in visions of an eternal abyss. On a failed save, the creature is incapacitated for 1 minute and takes 50 (10d10) psychic damage each turn. It can repeat the saving throw at the end of each of its turns, ending the effect on a success.

Call of the Abyss (Recharge 6). The Avatar emits a deafening call from beyond the waves. Creatures within 100 ft. must make a DC 27 Constitution saving throw. On a failed save, a creature takes 70 (10d12) thunder damage, is stunned for 1 minute, and is deafened permanently. On a successful save, the creature takes half as much damage, and is deafened until the start of its next turn.

Tidecaller’s Gift. The Avatar has control over water and its creatures. As a bonus action, she can summon a massive tidal wave or whirlpool (100 ft. diameter) within 300 ft. of her. This effect lasts for 3 rounds. Creatures within the area must make a DC 27 Dexterity saving throw. On a failed save, they take 60 (10d12) bludgeoning damage and are restrained by the water. On a successful save, they take half damage and are not restrained.

Leviathan can take 6 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. Leviathan regains spent legendary actions at the start of its turn.

Detect. The Avatar makes a Wisdom (Perception) check.

Tail Strike. The Avatar makes a tail attack.

Maelstrom (Costs 2 Actions). The Avatar conjures a localized maelstrom within 60 ft. of her. Each creature within that area must succeed on a DC 26 Strength saving throw or be pulled 30 ft. toward the center and take 44 (8d10) bludgeoning damage.

If Leviathan’s Oceanic Awakening trait has activated in the last hour, it can use the options below as legendary actions.

Rebuke of Tides (Costs 2 Actions). The Avatar channels a wave of divine energy, knocking creatures near her away. Creatures within 30 ft. must succeed on a DC 25 Dexterity saving throw or be pushed 60 ft. away and take 36 (6d10) force damage.

Leviathan’s Command (Costs 3 Actions). All creatures controlled or summoned by the Avatar (aquatic or otherwise) act immediately, gaining an additional action on their next turn. This includes making one melee attack or moving up to half their movement speed.

Abyssal Vortex (Costs 3 Actions). The Avatar summons a vortex of abyssal water at a point she can see within 200 ft. All creatures within a 30 ft. radius must succeed on a DC 27 Strength saving throw or be lifted and restrained by the vortex. The creatures can attempt to escape the vortex on their turn by succeeding on a DC 26 Dexterity saving throw. The vortex lasts until the Avatar chooses to end it.