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Ancient Sea Dragon

Gargantuan · Dragon · CR 22 · Neutral Evil

Source. Tome of Beasts

22 (natural armor)

481 (26d20+208)

Ability Scores

Core attributes and their modifiers.

STR

DEX

CON

INT

WIS

CHA

Overview

Category Monsters

Size Gargantuan

Type Dragon

Alignment Neutral Evil

XP 41000

Initiative Bonus +0

Movement

Walk 40 ft (12.2 m)

Fly 80 ft (24.4 m)

Swim 80 ft (24.4 m)

Climb 20 ft (6.1 m)

Crawl 20 ft (6.1 m)

Senses

Darkvision 120 ft (36.6 m)

Blindsight 60 ft (18.3 m)

Passive Perception 27

Saving Throws

Dexterity +7 Constitution +15 Wisdom +10 Charisma +12

Skills

Perception +17 Stealth +7

Languages

Common, Draconic, Infernal, Primordial

Resistances & Immunities

Damage Immunities

cold

Environments

Ocean

Traits

Amphibious

The dragon can breathe air and water.

Legendary Resistance (3/Day)

If the dragon fails a saving throw, it can choose to succeed instead.

Regional Effects

the region containing a legendary sea dragon's lair is warped by the dragon's magic, which creates one or more of the following effects:

Sea life becomes richer within 6 miles of the lair. Schools of fish move into new waters, sharks become common, and whale migration paths shift to pass near the area.
Water temperatures drop sharply within 6 miles of the lair. Creatures not accustomed to cold suffer exposure to extreme cold while swimming in this water.
Storms and rough water are more common within 6 miles of the lair.

if the dragon dies, conditions of the sea surrounding the lair return to normal over the course of 1d10 days.

Sea Dragon's Lair

on initiative count 20 (losing initiative ties), the dragon takes a lair action and generates one of the following effects. The dragon can't use the same effect two rounds in a row:

Four vortexes, each 5 feet in diameter and up to 30 feet tall, appear within the lair where the dragon wishes. Creatures occupying the space where a vortex appears or who enter the vortex for the first time on a turn must make a DC 15 Dexterity save or be restrained. As an action, a creature can free itself or another creature from a vortex by succeeding on a DC 15 Strength check. The vortexes last until the dragon uses this lair action again or until the dragon dies.
The dragon creates a wall of living coral on a solid surface it can see within 120 feet of it. The wall can be up to 30 feet long, 30 feet high, and 1 foot thick. When the wall appears, each creature within its area takes damage as if touching the wall and is pushed 5 feet out of the wall's space, on whichever side of the wall it wants. Touching the wall releases painful stings that deal 18 (4d8) poison damage, or half that with a successful DC 15 Constitution saving throw. Each 10-foot section of the wall has AC 5, 30 hit points, resistance to fire damage, and immunity to psychic damage. The wall lasts until the dragon uses this lair action again or until the dragon dies.
The dragon bends time around its enemies. Four creatures the dragon can see within 120 feet of it must succeed on a DC 15 Wisdom save or be affected by a slow spell. This effect last until initiative count 20 on the following round.

Siege Monster

The dragon deals double damage to objects and structures.

Actions

Bite

+16 to hit, reach 15 ft (4.6 m). Hit: 2d10 cold damage.

Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 20 (2d10 + 9) piercing damage plus 11 (2d10) cold damage.

Claw

+16 to hit, reach 10 ft (3 m). Hit: 2d6 slashing damage.

Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 16 (2d6 + 9) slashing damage.

Frightful Presence

Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 20 Wisdom saving throw or become frightened for 1 minute. A creature repeats the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Multiattack

The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Tail

+16 to hit, reach 20 ft (6.1 m). Hit: 2d8 bludgeoning damage.

Melee Weapon Attack: +16 to hit, reach 20 ft., one target. Hit: 18 (2d8 + 9) bludgeoning damage.

Tidal Breath

Recharge 5–6

The dragon exhales a crushing wave of frigid seawater in a 90-foot cone. Each creature in that area must make a DC 23 Dexterity saving throw. On a failure, the target takes 44 (8d10) bludgeoning damage and 44 (8d10) cold damage, and is pushed 30 feet away from the dragon and knocked prone. On a successful save the creature takes half as much damage and isn't pushed or knocked prone.

Wing Attack (Costs 2 Actions)

The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 24 Dexterity saving throw or take 16 (2d6 + 9) bludgeoning damage and be knocked prone. The dragon can then move up to half its flying speed, or swim speed if in the water.

Legendary Actions

Detect

Cost 1

The dragon makes a Wisdom (Perception) check.

Tail Attack

Cost 1

The dragon makes a tail attack.

Wing Attack

Cost 2

About Ancient Sea Dragon

Ancient Sea Dragon is a gargantuan dragon with a Challenge Rating of 22. It has a neutral evil alignment.

In combat, this creature maintains an Armor Class of 22 and possesses 481 hit points (derived from 26d20+208).

Ancient Sea Dragon has communication capabilities including Common, Draconic, Infernal, Primordial. This allows it to interact verbally with various creatures and characters.

GM Tips: Using Ancient Sea Dragon

3 tips available

When using Ancient Sea Dragon in your D&D 5e campaign, consider these tactical approaches:

Flight Control Strategy: Target flying creatures with spells like 'Hold Person', 'Web', or 'Grease' to ground them. Without flight restriction, they can escape melee range easily. Consider area denial spells below their flight altitude to force them into disadvantageous positions.
Aquatic Combat: This creature can swim at 80 ft. It has advantage in water environments. Consider fighting on land or using water-based spells against it.
Cold Damage Strategy: Cold-based attacks can slow or freeze. Prepare 'Heat Metal' or fire spells as countermeasures. Ice terrain can be used to create difficult terrain for melee characters.

Player Guide: Facing Ancient Sea Dragon

3 strategies available

When your party encounters this creature, keep these strategies in mind:

Counter Flight Advantage: This creature can fly! Use ranged attacks, reach weapons, or spells like 'Thunderwave' to push it away. Consider 'Gust of Wind' or 'Earthbind' to ground it. Melee characters need fly speed or flight magic to engage.
Aquatic Combat Defense: This creature can swim at 80 ft! It has advantage in water. Fight on land if possible. Use 'Control Water' or drain water sources to limit its mobility.
Cold Damage Protection: This creature deals cold damage! Get cold resistance or use fire spells. Avoid water surfaces - they can freeze and create difficult terrain. 'Heat Metal' can counter cold.

Encounter Building Calculator

Standard Party Encounter (4-5 characters):

This creature is a medium encounter for a party of 4 characters of level 22.

High-Level Solo Encounter:

This creature is too powerful for a single level-20 character. You need 3.0 character(s) at maximum level (20) to face this creature.

Experience Point Thresholds:

Medium: 50,600 XP
Hard: 75,900 XP
Deadly: 101,200 XP

Based on D&D 5e Dungeon Master's Guide encounter building guidelines. CR roughly equals party level for medium encounters.

Frequently Asked Questions

What is the challenge rating of Ancient Sea Dragon?: Ancient Sea Dragon has a Challenge Rating of 22, making it appropriate for parties of level 22.0.
What type of creature is Ancient Sea Dragon?: Ancient Sea Dragon is a Gargantuan Dragon, which affects how certain spells and abilities interact with it.
What languages does Ancient Sea Dragon speak?: Ancient Sea Dragon can communicate in Common, Draconic, Infernal, Primordial.