Black Shuck

Blood Frenzy. The black shuck has advantage on attack rolls against any creature that doesn't have all its hp.

Keen Hearing and Smell. The black shuck has advantage on Wisdom (Preception) checks that rely on hearing or smell.

Water Walker. The black shuck can move across the surface of water as if it were harmless, solid ground. This trait otherwise works like the water walk spell.   

Multiattack. The black shuck makes three Bite attacks and can use Curse of the Grave or Fearsome Howl, if available. If at least two Bite attacks hit a medium or smaller target, the black shuck sinks in its teeth, shaking its head violently, and the target much succeed on a DC 17 strength saving throw or take 7 (2d6) slashing damage and be thrown up to 15 feet in a random direction and knocked prone.

Bite. Melee Attack Roll: +8, reach 5 ft. Hit: 13 (2d8 + 4) Piercing damage and 10 (3d6) necrotic damage.

Curse of the Grave. The black shuck glares at one creature it can see within 30 feet of it. The target must succeed on a DC 17 Wisdom saving throw or be cursed A cursed creature has disadvantage on the next two death saving throws it makes in the next 7 days. The curse lasts until the cursed creature has made two death saving throws, until 7 days have passed, or until it is lifted by a remove curse spell or similar magic.

Fearsome Howl (Recharge 5-6). The black shuck howls a haunting tune. Each creature within 60 feet of the black shuck that can hear the howl must succeed on a DC 17 Wisdom saving throw or become frightened until the end of its next turn. A frightened creature that is concentrating on a spell must succeed on a DC 17 Constitution saving throw or it loses concentration.

Mist Stalker. While in an area of dim light, fog, or mist, the black shuck takes the Hide action.