Amphibious. The  Wretchfin can breathe air and water.

Negative Energy Aura. Creatures within 30 feet of the  Wretchfin can’t regain hit points, and any creature that starts its turn within 30 feet of the Wretchfin takes 10 3d6 necrotic damage.

If the Wretchfin is struck with a critical hit the attacking player can cut the Wretchfin’s esca lure instead of dealing damage. If its esca lure is cut, the  Wretchfin loses this feature.

Multiattack. Wretchfin makes two attacks: one with its bite and one with its tail. 

Bite. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 26 (3d12 + 7) piercing damage.

Tail. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 26 (3d12 + 7) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be pushed up to 10 feet away from the Wretchfin and knocked prone.

Ray of Cold. Ranged Spell Attack: +12  to hit, range 120 ft., one target. Hit: 21 4d6 cold damage

Death-Ink Breath (Recharge 6). The Wretchfin expels a spray of inky black fluid from sacks in its mouth in a 30-foot cone. Each creature in that area must make a DC 14 Dexterity saving throw. On a failed save, the creature takes 22 4d10 necrotic damage and is Blinded. On a successful save, the creature takes half as much damage and isn't blinded.

Necromantic energy washes over all enemy creatures that Wretchfin can see within range, draining moisture and vitality from it. The targets must make a Constitution saving throw. The target takes 10d8 necrotic damage on a failed save, or half as much damage on a successful one. This spell has no effect on undead or constructs.

If a plant creature or a magical plant is within range, it makes the saving throw with disadvantage, and the spell deals maximum damage to it.

If a nonmagical plant that isn't a creature  is within range, such as a tree or shrub, it doesn't make a saving throw; it simply withers and dies.