Gargantuan monstrosity, unaligned

Armor Class 19 (natural armor)
Hit Points 310 (20d20+100)
Speed 40 ft., swim 80 ft.

27 (+8) 20 (+5) 20 (+5) 13 (+1) 13 (+1) 12 (+1)

Saving Throws Int+8, Wis+8, Cha+8
Skills Athletics +15, Perception +15, Stealth +12, Survival +15
Damage Vulnerabilities lightning
Damage Resistances acid, fire, thunder; bludgeoning, piercing, slashing
Damage Immunities cold, poison
Condition Immunities charmed, exhaustion, frightened, petrified, poisoned, stunned
Senses darkvision 300 ft., passive Perception 25
Languages telepathy 200 ft.
Challenge 23 (50,000 XP)


  • Dark Sight. Magical darkness doesn’t impede the marwolaeth’s darkvision.
  • Freedom of Movement. The marwolaeth ignores difficult terrain, and magical effects can’t reduce its speed or cause it to be restrained. It can spend 5 feet of movement to escape from nonmagical restraints or being grappled.
  • Hatchlings. A 30-foot radius cloud of parasitic offspring surrounds the marwolaeth. A creature that starts its turn in the area or first enters into the area on a turn must make a DC 20 Dexterity saving throw. On a failure, it takes 14 (4d6) piercing damage and is poisoned until the beginning of its next turn. Humanoids that take 30 or more damage from Hatchlings become infected with marwolaeth spores which turn them into marwolaeths after 1d4 weeks without magical healing or invasive surgery.
  • Legendary Resistance (3/Day). If the marwolaeth fails a saving throw, it can choose to succeed instead.
  • Magic Weapons. The marwolaeth weapon attacks are magical.
  • Regeneration. The marwolaeth regains 30 hit points at the start of its turn. If it takes lightning damage, this trait doesn’t function at the start of the marwolaeth’s next turn. The marwolaeth dies only if it starts its turn with 0 hit points and doesn’t regenerate.
  • Siege Monster. The marwolaeth deals double damage to objects and structures.
  • Trample. The marwolaeth can use a bonus action to overrun creatures of Huge size or smaller, moving up to half its speed without provoking opportunity attacks. Creatures in the marwolaeth’s path or sharing its space at the end of its movement make a DC 23 Dexterity saving throw. On a failure, a creature takes 26 (4d8+8) bludgeoning damage and is knocked prone.


A marwolaeth begins combat by hitting the maximum number of targets with a sonic roar before using trample. Once within range of multiple targets, the marwolaeth grabs spellcasters and swallows them. The creature detects and engages the PCs when they are about a quarter of a mile away from the city and they near immediately after killing the creature.


  • Multiattack. The marwolaeth uses its Frightful Presence. It then attacks three times: once with its bite and twice with its claws.
  • Bite. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 24 (3d10+8) piercing damage.
  • Claws. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 22 (4d6+8) slashing damage. If the target is a creature it is grappled (escape DC 23).
  • Sonic Roar (Recharge 4-6). The marwolaeth erupts with sound that travels in a 90-foot cone. Each creature in that area must make a DC 23 Dexterity saving throw, taking 90 (20d8) thunder damage on a failed save, or half as much damage on a successful one.
  • Swallow. The marwolaeth makes one bite attack against a Huge or smaller creature it is grappling. If the attack hits, that creature takes the bite’s damage and 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 marwolaeth, and it takes 28 (8d6) acid damage at the start of each of the marwolaeth’s turns. If the marwolaeth takes 40 damage or more on a single turn from a creature inside it, the marwolaeth must succeed on a DC 15 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 marwolaeth. If the marwolaeth dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 40 feet of movement, exiting prone.


These massive creatures are far less organic than their terrifying visage might lead one to believe, composed of a strange, otherworldy mix of cybernetics and fell genetics.

Marwolaeth all begin their existence as a humanoid of some kind (one unfortunate enough to have encountered one of the creatures) but each evolves to look slightly distinct from its kin. Regardless of the monster’s appearance, these predators of the world’s deepest waters are some of the deadliest entities on the planet, their very bodies designed to endlessly prowl the ocean floor at the behest of subtle directives encoded by unfathomable overlords millennia ago.

Jutting out of the underwater mountain you’ve been steadily swimming up is a titanic outcropping of pipes, structures, and streets made entirely from metallic coral or crustacean plates. All of the mammoth settlement sits neatly under a field of energy similar to the anomaly far behind you and with some relief, you draw closer to dry land-or the closest thing you’ll find to it under the waves-once more.

Rippling cords of hardened red muscles make up the enormous limbs of the monster that towers before you, easily the size of a country estate. Above its six glowing eyes is a blackened carapace laced with metallic engravings and circuitry that extends down along its shoulders and across its back.

Section 15: Copyright Notice

Epic Depths © 2021 Mike Myler, published under license by Legendary Games.

This is not the complete section 15 entry - see the full license for this page