Aura of Decay. Any creature other than a Nuckelavee that starts its turn within 10 feet of the Nuckelavee must succeed on a DC 16 Constitution saving throw or be poisoned until the start of the creature's next turn. On a successful saving throw, the creature is immune to the aura of decay for 1 hour.
Charge. If the Nuckelavee moves at least 30 feet straight toward a target and then hits it with a claw attack on the same turn, the target takes an extra 10 (3d6) piercing damage.
Enraged Attacks: If the Nuckelavee detects the scent of burning seaweed, at the beginning of it's turn, the Nuckelavee gains advantage on all melee weapon Attack Rolls it makes during that turn, but Attack Rolls against it have advantage until the start of its next turn. During this rage, the Nuckelavee must target the person or origin of the burning seaweed, forsaking its safety in it's blind rage.
Fresh-Water Vulnerability. The Nuckelavee cannot stand the touch of Fresh Water against its exposed skin. The Nuckelavee takes 20 acid damage if it ends its turn in freshwater (this includes exposure to the rain).
If a Nuckelavee takes damage from a spell that produces non-salinated water, the Nuckelavee counts as vulnerable to that damage.
Multiattack. The Nuckelavee makes two attacks: one with its Claws and one with its Bite or one with its Hooves and one with its Claws.
Claw. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 9 (1d10 + 4) slashing damage.
Hooves. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage.
Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) piercing damage. A target creature must must make a DC 16 Constitution saving throw, taking 7 (2D6) poison damage and becoming poisoned until the start of the creature's next turn on a failure or half as much damage and resisting the poisoned condition on a success.
Mortasheen (Recharge 5-6). The Nuckelavee exhales a blast of decaying breath in a 60-foot cone. Each creature in that area must make a DC 16 Constitution saving throw, taking 36 (8d8) necrotic damage on a failed save, or half as much damage on a successful one. If the saving throw fails by 5 or more, a target instead takes 64 necrotic damage. The target dies if reduced to 0 hit points by this ray.
Equine creatures, including Centaurs have disadvantage on this saving throw.
Description
This creature is said to resemble a horse and its rider who have both been flayed and while they may at first appear to be two creatures, they are instead one! The “rider” part of this creature, ends at the waist, with no legs to be seen. This torso sprouts from the spine of the horse-like body’s back, to give the illusion of something familiar to a passer in the night, but it’s only on closer inspection that the true horror of this creature is revealed.
Often called "The devil of the sea", the Nuckelavee emerges from the ocean on dry evenings, for it fears the touch of rain and freshwater against its skinless flesh. Once on land, it hunts any and all creatures it can find, decaying and rotting crops, spreading plagues throughout local livestock and disembowelling any mortal creatures it can find, before it slinks away back into the ocean to return another night.
Is there any reason to ever use the hooves attack? Bite is just better in every way. You can multiattack with bite just like you would with hooves, bite does the same damage as hooves, bite inflicts poison unlike hooves
its just better in every way
Maybe give it a charging/trample attack that gives a bonus to hoof damage if the monster can run over their target after moving? Possibly inflict the prone condition so it can bite and claw with advantage as it stands over the target it just trampled?