Cerberus

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.

Keen Heads. Advantage on all perception checks.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 7 (2d6) fire damage.

Fire Breath (Recharge 5–6). The hound exhales fire in a 15-foot cone. Each creature in that area must make a DC 12 Dexterity saving throw, taking 21 (6d6) fire damage on a failed save, or half as much damage on a successful one.

Multi Headed Pact Tactics. Once per turn Cerberus can gain pact tactics from one of its other heads on a single attack.

MultiAttack. Cerberus makes two bite attacks.

Searing Counter. When an enemy attacks Cerberus, it can use it’s reaction to use its Fire Breath.