Adult Sea Dragon

Huge dragon, Neutral Evil

Armor Class

19 (natural armor)

Hit Points

225 (18d12+108)

Speed

walk 40 ft., fly 80 ft., swim 60 ft.

Saves

Dex +5, Con +11, Wis +7, Cha +9

Skills

Perception +12, Stealth +5

Damage Immunities

cold

Languages

Common, Draconic

Challenge

16

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

Multiattack

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

Bite

Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 18 (2d10 + 7) piercing damage plus 5 (1d10) cold damage.

Claw

Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 7) slashing damage.

Tail

Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 16 (2d8 + 7) bludgeoning 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 17 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.

Tidal Breath (Recharge 5-6)

The dragon exhales a crushing wave of frigid seawater in a 60-foot cone. Each creature in that area must make a DC 19 Dexterity saving throw. On a failure, the target takes 33 (6d10) bludgeoning damage and 33 (6d10) 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.

Legendary actions

The dragon can take 3 legendary actions, choosing from the options below

Only one legendary action option can be used at a time and only at the end of another creature's turn. The dragon regains spent legendary actions at the start of its turn.

Detect

The dragon makes a Wisdom (Perception) check.

Tail Attack

The dragon makes a tail attack.

Wing Attack (Costs 2 Actions)

The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 20 Dexterity saving throw or take 14 (2d6 + 7) bludgeoning damage and be knocked prone. The dragon can then move up to half its flying speed, or half its swim speed if in the water.