Vent Linnorm

Amphibious. The linnorm can breathe air and water.

Blood Scent. The linnorm can smell blood in the water within 5 miles of it. It can determine whether the blood is fresh or old and what type of creature shed the blood. In addition, the linnorm has advantage on Wisdom (Perception) and Wisdom (Survival) checks to find or track a creature that doesn't have all its hp.

Multiattack. The linnorm can use its Frightful Presence. It then makes three attacks: one with its bite and two with its tail.

Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 18 (2d10 + 7) piercing damage plus 14 (4d6) necrotic damage.

Tail. Melee Weapon Attack: +12 to hit, reach 20 ft., one target. Hit: 16 (2d8 + 7) bludgeoning damage. The target is grappled (escape DC 18) if it is a Large or smaller creature and the linnorm doesn't have two other creatures grappled. Until this grapple ends, the target is restrained.

Frightful Presence. Each creature of the linnorm's choice that is within 120 feet of the linnorm and aware of it must succeed on a DC 16 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 the creature's saving throw is successful or the effect ends for it, the creature is immune to the linnorm's Frightful Presence for the next 24 hours.

Inky Breath (Recharge 5-6). The linnorm exhales a cloud of briny ink in a 60-foot cone. Each creature in that area must make a DC 19 Constitution saving throw. On a failure, a creature takes 52 (15d6) necrotic damage and is blinded for 1 minute. On a success, a creature takes half the damage and isn't blinded. A blinded creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.