Keen Smell. The hound has advantage on Wisdom (Perception) checks that rely on smell.

Pack Tactics. The hound has advantage on an attack roll against a creature if at least one of the hound's allies is within 5 feet of the creature and the ally isn't incapacitated.

Language memorization. The hound instantly learns any language it hears other than languages in already knows or celestial, infernal, and abyssal.

Language allergies.  If the hound hears the language celestial they will not be able to get within 10 feet of the creature that spoke it for 5 turns and it will take 4 (2d4) radiant damage.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) piercing damage. If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone.

Claws. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) piercing damage. If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone.

Shriek (Recharge 5–6). The hound makes a piercing scream. Each creature that can hear it must make a DC 12 Constitution saving throw, taking 16 (4d8) force damage on a failed save, or half as much damage on a successful one.