Aneth's Hound

Keen Hearing and Smell. The hound has advantage on Wisdom (Perception) checks that rely on hearing or 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.

Fiendish Resiliance. The hound regains 6 hit points at the start of its turn. If the hound takes radiant damage or damage from a silvered weapon, this trait doesn't function at the start of the hound's next turn. 

Multiattack. The hound makes two bite attacks, or one bite attack and one use of its fire breath.

Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 14 (2d8 + 5) piercing damage plus 14 (4d6) fire damage.

Fire Breath. The hound exhales fire in a 15-foot cone. Each creature in that area must make a DC 17 Dexterity saving throw, taking 21 (6d6) fire damage on a failed save, or half as much damage on a successful one.

Emerald Eye (recharge 5-6). The hound fixes a creature within 300 feet of it with a searing gaze. That creature must make a DC 17 Constitution saving throw or take 21 (6d6) fire damage and become paralyzed for 1 minute. On a successful saving throw, a creature takes half as much damage and isn't paralyzed. A paralyzed creature can repeat its Constitution saving throw at the end of each of its turns, ending the effect on a success.

Frenzy. The first time the hound takes damage in a round, it must make a bite attack against every creature within 5 feet of it.