Arcane Leviathan

Gargantuan construct, unaligned

Armor Class 17 (natural armor)
Hit Points 279 (18d20 + 90)
Speed 10 ft., swim 60 ft.

26 (+8) 5 (–3) 21 (+5) 5 (–3) 17 (+3) 8 (–1)

Saving Throws Str +13, Con +10, Int +2, Wis +8, Cha +4
Damage Resistances acid, thunder; bludgeoning, piercing, and slashing from nonmagical attacks
Damage Immunities lightning, poison, psychic
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, paralyzed, petrified, poisoned
Senses truesight 120 ft., passive Perception 13
Languages understands the languages of its creator but can’t speak
Challenge 16 (15,000 XP)
Proficiency Bonus +5


  • Construct Nature. The arcane leviathan doesn’t require air, food, drink, or sleep.
  • Impregnable. If the arcane leviathan is subjected to an effect that allows it to make a saving throw to take only half damage, the leviathan instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.
  • Siege Monster. The arcane leviathan deals double damage to objects and structures.


  • Multiattack. The arcane leviathan makes one Slam attack and two Claw attacks, or it makes four Lightning Bolt attacks.
  • Claw. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 26 (4d8 + 8) slashing damage. If the target is Huge or smaller, it is grappled (escape DC 19). The leviathan has two claws, each of which can grapple only one target.
  • Slam. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 18 (4d4 + 8) bludgeoning damage, and the target must succeed on a DC 19 Strength saving throw or be knocked prone.
  • Lightning Bolt. Ranged Spell Attack: +8 to hit, range 150/600 ft., one target. Hit: 17 (4d6 + 3) lightning damage.
  • Pylon Discharge (Recharge 5–6). The leviathan discharges a surge of energy at a point the leviathan can see within 200 feet of it. Each creature within 30 feet of that point must make a DC 19 Dexterity saving throw. On a failure, a creature takes 45 (10d8) lightning damage and is blinded until the end of its next turn. On a success, a creature takes half the damage and isn’t blinded.


Lightning splits the sky on a clear day; the ocean breaks, and the leviathan wakes, a crustacean shape of ceramic armor and wrathful magic. Faded script in a forgotten tongue crawls along its flanks. Armor plating on its back parts as crystal pillars rise, charged with magic.

Long ago, an undersea civilization forged guardians for its great cities. They built these leviathans in the image of ancient gods, inscribing the armored carapaces with religious iconography and verses from scripture, arming the constructs with claws that could crush stone. Most fearsome of all, the creators built enormous magical weapons into the leviathans’ abdomens, meant to shatter armies and destroy cities if their masters were ever truly threatened. Eventually, their masters faded from the world, then from memory, and the leviathans became dormant.

Wrathful Relics. Occasionally, a leviathan awakens. With its cities ruined, the construct follows ancient retributive?strike protocols. It patrols the seas, looking for possible culprits to avenge itself upon or successor states to protect.

Sometimes, an arcane leviathan guards some undersea settlement or ancient ruin. Other times, it becomes a scourge of shipping lanes, destroying fleets and terrorizing docks of those who have infringed upon the territory of a nation dead for millennia.

Section 15: Copyright Notice

Tome of Beasts 3 © 2022 Open Design LLC; Authors: Eytan Bernstein, Celeste Conowitch, Benjamin L. Eastman, Robert Fairbanks, Scott Gable, Basheer Ghouse, Richard Green, Jeremy Hochhalter, Jeff Lee, Christopher Lockey, Sarah Madsen, Ben Mcfarland, Jonathan Miley, Kelly Pawlik, Sebastian Rombach, Chelsea Steverson, Brian Suskind, Mike Welham

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