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Ancient Sea Dragon

Gargantuan · Dragon · CR 23 · Neutral Evil

Source. Tome of Beasts 1 (2023 Edition)

22 (natural armor)

518 (28d20 + 224)

Ability Scores

Core attributes and their modifiers.

STR

DEX

CON

INT

WIS

CHA

Overview

Category Monsters

Size Gargantuan

Type Dragon

Alignment Neutral Evil

XP 50000

Initiative Bonus +0

Movement

Walk 80 ft (24.4 m)

Fly 40 ft (12.2 m)

Swim 40 ft (12.2 m)

Climb 40 ft (12.2 m)

Crawl 40 ft (12.2 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, Primordial

Resistances & Immunities

Damage Immunities

cold

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.

Siege Monster

The dragon deals double damage to objects and structures.

Actions

Bite

+16 to hit, reach 15 ft (4.6 m). Hit: 2d10+9 plus 4d6 cold damage.

Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 20 (2d10 + 9) piercing damage plus 14 (4d6) cold damage.

Fin

+16 to hit, reach 10 ft (3 m). Hit: 2d6+9 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 can repeat 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 uses its Frightful Presence. It then makes one Bite attack and two Fin attacks.

Tail

+16 to hit, reach 20 ft (6.1 m). Hit: 2d8+9 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 creature takes 44 (8d10) bludgeoning damage and 44 (8d10) cold damage and is pushed up to 45 feet away from the dragon and knocked prone. On a success, the creature takes half the damage and isn't pushed or knocked prone.

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

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 swimming speed if in the water.

About Ancient Sea Dragon

Ancient Sea Dragon is a gargantuan dragon with a Challenge Rating of 23. It has a neutral evil alignment.

In combat, this creature maintains an Armor Class of 22 and possesses 518 hit points (derived from 28d20 + 224).

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

GM Tips: Using Ancient Sea Dragon

2 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.
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

2 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.
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 23.

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: 55,200 XP
Hard: 82,800 XP
Deadly: 110,400 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 23, making it appropriate for parties of level 23.0.
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, Primordial.