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The Hull-Breaker Behemoth - AI-generated fantasy Monster

The Hull-Breaker Behemoth

Originally a specimen in an arcane filtration experiment, the Behemoth outlived its creators. It learned to manipulate the Sanctum's water valves, turning the facility's defense systems into its personal hunting tools.

Monsters
Gargantuan monstrosity · Deadly · Unique

The Hull-Breaker Behemoth

A gargantuan, salt-encrusted lobster mutated by alchemical runoff and mechanical sludge, acting as the apex predator of a decaying desalination plant.
AC19
HP232/232
CRDeadly
Init
STR
DEX
CON
INT
WIS
CHA
ConditionsNone

Combat

AC 19 · HP 232 · Deadly

The Hull-Breaker Behemoth

Gargantuan monstrosity (mutant), neutral
Armor Class19 (Natural Armor)
Hit Points232 (16d20 + 64)
Speed
30 ft. walk,
60 ft. swim
STR
DEX
CON
INT
WIS
CHA
Saving ThrowsSTRCONWIS
SkillsPerceptionAthletics
Damage Resistances
Cold,
Bludgeoning, Piercing, and Slashing from Nonmagical Attacks
Immunities
Poison
Weaknesses
Thunder
Senses
Blindsight 60 ft.,
Darkvision 120 ft.,
Passive Perception 17
Languages
None (can understand rudimentary commands in Primordial)
ChallengeDeadly
Gilded Carapace. Whenever a creature hits the Behemoth with a melee attack, it must succeed on a Wisdom saving throw or become dazzled by the light reflecting off the coins until the end of its next turn. While dazzled, it has disadvantage on attack rolls.
Amphibious. The Behemoth can breathe air and water.
Siege Monster. The Behemoth deals double damage to objects and structures.

Actions

Multiattack. The Behemoth makes two Claw attacks. It can replace one Claw attack with a use of Tidal Wave if available.
Claw. Melee Weapon Attack: to hit, reach 15 ft., one target. Hit: 25 () bludgeoning damage, and the target is grappled (escape ). The Behemoth has two claws, each of which can grapple one target.
Crushing Pincer. The Behemoth deals 35 () bludgeoning damage to a creature it is grappling. The target must succeed on a Constitution saving throw or be stunned until the end of the Behemoth's next turn.
Tidal Wave (Recharge 5-6). The Behemoth slams its tail into the water, creating a 60-foot cone of high-pressure liquid. Each creature in that area must make a Strength saving throw. On a failure, a creature takes 36 () bludgeoning damage and is pushed 40 feet away. If they hit a solid object (like the grinding vats), they take an additional 10 () damage. On a success, the damage is halved and the creature isn't pushed.

Reactions

Reactive Shell. When a creature within 15 feet hits the Behemoth with an attack, the Behemoth can snap its pincer at them, making one Claw attack.

Legendary Actions

Detect. The Behemoth makes a Wisdom (Perception) check.
Shift Position. The Behemoth moves up to half its speed without provoking opportunity attacks.
Blinding Bioluminescence (costs 2 actions). The Behemoth's eyes flare. Each creature within 30 feet that can see the Behemoth must succeed on a Constitution saving throw or be blinded until the end of its next turn.
Role
Solo Boss
Built for
11-14

Gear

  • Sun-Stone Encrustation (Treasure, 8000gp)Raw gold and gems fused into the shell.

Notes for the game master

The Behemoth is designed to split the party by using Tidal Wave to push some members into the hazard zones (grinding vats) while grappling the others.

Tactics

  1. Opening

    Start with Tidal Wave to flush the squishy backline toward the hazards and separate them from the tanks.

  2. Mid-fight

    Grapple the two most dangerous martial combatants and use Crushing Pincer to stun them, effectively removing them from the turn order.

  3. End of the fight

    If heavily wounded, use Blinding Bioluminescence to retreat into the deeper water of the vats, pulling a grappled victim along to drown or crush.

  4. Retreat

    The Behemoth will not flee if there is significant gold nearby; it fights to the death to protect its 'hoard'.

How it fights

Focus on targets wearing heavy metal armor (attracted to the shine).
Use the environment to smash grappled targets against walls.
Keep back to the vats to prevent being flanked.

Who it attacks first

Paladins or Fighters (shiny armor)
Spellcasters using light-based spells
Anyone attempting to pry a coin from its shell

Works well with

Hazardous environment (Grinding Vats: 4d10 slashing damage per turn).
Slick floors (Acrobatics DC 14 to avoid falling prone).

How to beat it

Thunder damage (cracks the shell).
Freedom of Movement (negates the primary grapple threat).
Darkness spells (negates its light-based distractions).

Ways to avoid a fight

Distracting it by throwing large amounts of gold into the water.
Using Animal Handling (DC 25) to provide a better 'treasure' in exchange for safe passage.

Ecology

An enormous lobster-like horror spanning forty feet, its carapace is a patchwork of mottled indigo and rusted iron-plate. Dozens of gold coins, jewelry, and silver plates are fused into its shell. Two massive, asymmetrical claws click with mechanical force, and eight eyes glow with a sickly, pulsating neon-blue light.

Behavior

It is hyper-territorial and obsessed with the collection of 'sun-stones' (gold and gems). It spends most of its time clinging to the rusted pipes of the Desalination Sanctum, waiting for the vibrations of intruders to signal a 'contribution' to its shell.

How it lives

The Behemoth feeds on the organic sludge filtered by the plant's machinery but has developed a taste for the 'crunch' of metal-clad adventurers. Its presence has turned the local ecosystem into a graveyard of shipwrecks and bone.

Lair

The Desalination Sanctum, a flooded industrial complex filled with grinding vats, high-pressure steam pipes, and narrow catwalks.

Habitat
Coastal ruins, industrial sewers, desalination plants.

Signs that it is near

Massive drag marks in the salt-crust
Rhythmic metallic clanking sounds
Dull blue light reflecting off the water
Scattered, crushed gold coins in the silt

Tags

Aquatic,
Siege,
Bio-Luminescent

Lore

Originally a specimen in an arcane filtration experiment, the Behemoth outlived its creators. It learned to manipulate the Sanctum's water valves, turning the facility's defense systems into its personal hunting tools.

What drives it

To accumulate more gold to embed into its ever-growing shell and to defend the churning vats that provide its warmth.

After the fight

The Sanctum begins to destabilize without the Behemoth's weight holding certain valves down; the party must escape as the facility begins to flood.

Variants

Steam-Powered Behemoth: Swaps Tidal Wave for a Steam Breath (Fire Damage).
Abyssal Behemoth: Swaps resistances for Psychic immunity.

Hooks

Plot hooks

A famous merchant's flagship was pulled into the Sanctum by the 'Blue Glow'.
The desalination plant has stopped working because 'the pipes started screaming'.
A rogue artificer needs the mutated ichor from the Behemoth's brain.

How to use it

Final boss of an underwater or seaside dungeon.
A random encounter during a storm at a refinery.

Treasure

1400gp in loose coins
5 Emeralds (1000gp each)
A partially dissolved +1 Shield embedded in the shell

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