Black Shuck

Keen Senses. The black shuck has advantage on any Perception and Survival checks that rely on hearing and smell.

Multiattack. The black shuck makes three attacks per turn, two with it's claws and one with it's bite attack. Alternatively, the black shuck can make a Charging attack and one bite attack.

Claws. Melee Weapon Attack: +11 to hit, reach 5 ft., 1 target. Hit: 18 (3d6 + 7) slashing damage. 

Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., 1 target. Hit: 21 (3d8+7) piercing damage.

Charge. After moving at least 20 ft. towards a target the black shuck can make a claw attack. If the attack hits the black shuck deals an additional 22 (4d10) slashing damage and if the target is Huge or smaller it must succeed on a DC 19 Strength saving throw or be knocked prone and pinned by the black shuck. In order to escape the pin the pinned creature must succeed on a DC 19 Str (Athletics) or Dex (Acrobatics) check to escape the pin.

Iron Jaws. The black shuck makes a bite attack as it's opportunity attack. If this opportunity attack hits the targets movement is reduced to 0 for the rest of the round.