monster

Abyssal Leviathan

CR 26

Gargantuan Monstrosity (Titan), Neutral Evil

Reveal Stat Block

Armor Class

23 (Natural Armor)

Hit Points

585 (30d20 + 270)

Speed

20 ft., swim 90 ft.

str

+10

dex

con

int

wis

cha

Traits

Legendary Resistance (3/Day).If the leviathan fails a saving throw, it can choose to succeed instead.

Aether-Bleed Aura.The leviathan is surrounded by a 60-foot aura of unstable mana. Any creature that starts its turn in the aura must succeed on a DC 22 Constitution saving throw or take 14 (4d6) force damage. Additionally, within this aura, any spell of 5th level or lower has a 50 percent chance of failing, wasting the spell slot (as if affected by a Dead Magic Zone).

Siege Monster.The leviathan deals double damage to objects and structures.

Amphibious.The leviathan can breathe air and water.

Aether-Crystal Carapace.The leviathan has advantage on saving throws against spells and other magical effects, and any ranged spell attack that misses it is reflected back at the caster, using the caster's attack roll and modifiers.

Actions

Multiattack.The leviathan can use its Frightful Presence. It then makes three attacks: one with its bite and two with its slams. It can replace its bite with Swallow.

Bite.Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 36 (4d12 + 10) piercing damage plus 13 (3d8) force damage. If the target is a Large or smaller creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the leviathan can't bite another target.

Slam.Melee Weapon Attack: +18 to hit, reach 20 ft., one target. Hit: 28 (4d8 + 10) bludgeoning damage.

Aether-Storm Roar (Recharge 5–6).The leviathan emits a resonant, magical roar in a 90-foot cone. Each creature in that area must make a DC 25 Constitution saving throw. On a failed save, a creature takes 77 (22d6) force damage and is stunned until the end of its next turn. On a successful save, a creature takes half as much damage and isn't stunned. Additionally, any active spell effects of 6th level or lower in the cone are dispelled.

Swallow.The leviathan makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the bite's damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the leviathan, and it takes 42 (12d6) acid damage plus 21 (6d6) force damage at the start of each of the leviathan's turns. If the leviathan takes 60 damage or more on a single turn from a creature inside it, the leviathan must succeed on a DC 25 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the leviathan. If the leviathan dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

Abyssal Leviathan

A gargantuan sea monster mutated by raw aether leaking from the Abyssal Trench. Its scales are hardened like aether-crystals, and its roar can summon localized mana-storms. It is a terrifying threat to any vessel in the Broad Swells, capable of swallowing galleons whole and shattering the foundations of coastal fortresses.

The Abyssal Leviathan is not merely an animal; it is an elemental manifestation of the ocean's fury, warped by the unstable energies of the Aether-Bleed. Its presence creates "Wild Magic Squalls" and unpredictable weather patterns for miles around its hunting grounds.

Secret Motivation: The Leviathan is drawn to the "Song of the Trench"—a rhythmic vibration coming from a buried precursor machine at the bottom of the Abyssal Trench. It believes it is protecting the machine, which is actually a terraforming device slowly turning the ocean into a liquid-aether soup.

Adventure Hook: The trade routes between the Eastern and Northern continents have been completely severed. The Gilded Corsairs are offering a king's ransom to anyone who can slay the "King of the Swells" and retrieve a shard of its heart-crystal to power a massive new illusion and cloaking artifact.