Leviathan (5e Creature)
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Gargantuan dragon, chaotic neutral
Saving Throws Str +18, Dex +10, Con +17, Int +12, Wis +10
Amphibious. The leviathan can breathe air and water.
Freedom of Movement. The leviathan ignores difficult terrain, and magical effects can't reduce its speed or cause it to be restrained. It can spend 5 feet of movement to escape from nonmagical restraints or being grappled.
Legendary Resistance (3/Day). If the leviathan fails a saving throw, it can choose to succeed instead
Siege Monster. The leviathan does double damage on objects and structures.
Multiattack. The leviathan uses its Frightful Presence. It then makes three attacks: one with its bite and two with its claws. It can use its Swallow instead of its bite.
Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage. If the target is a creature it is grappled (escape DC 20). Until the grapple ends, the target is restrained, and the leviathan can't bite another target.
Claw. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 17 (2d6 + 10) slashing damage.
Tail. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage.
Frightful Presence. Each creature of the leviathan's choice within 120 feet of the leviathan 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 turn, ending the effect on itself on a success. If a creature's saving throw is successful or the effects ends for it, the creature is immune to the Leviathan's Frightful Presence for 24 hours.
Steam Breath (Recharge 5-6). the Leviathan exhales a stream of hot steam in a 120 foot cone. Each creature in the area must make a DC 24 Dexterity saving throw, taking 42 (12d6) cold damage and 42 (12d6) fire damage on a failed save, or half as much on a successful one.
Swallow. The leviathan makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the bite's damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the leviathan, and it takes 42 (12d6) acid damage at the start of each of the leviathan's turns.
The leviathan can take 3 legendary actions, choosing form 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 leviathan regains spent legendary actions at the start of its turn.
Detect. The leviathan makes a Wisdom (Perception) check.
The leviathan is an immense dragon-like sea creature, 300 to 500 feet long. It is the lord of all seas and the intermediary between aquatic creatures and the gods.
On initiative count 20 (losing initiative ties), the leviathan takes a lair action to cause one of the following effect; the leviathan can't use the same effect two rounds in a row:
The region containing a legendary leviathan's lair is warped by the leviathans magic, which creates one or more of the following effects:
If the leviathan dies, these effects fade over the course of 1d10 days.