Cerberus

Aggressive. As a bonus action, the cerberus can move up to its speed toward a hostile creature that it can see.

Multiheaded. The cerberus can’t be surprised, and it has advantage on saving throws against being knocked unconscious.

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

Wildfire (Recharges after a Short or Long Rest). When the cerberus would be reduced to 12 or fewer hit points, it first gains 6 temporary hit points. If it survives, each of its three heads exhales fire in a 15- foot cone. Each creature in those areas must make a DC 13 Dexterity saving throw, taking 24 (7d6) fire damage on a failed save, or half as much damage on a successful one. Any flammable objects in the areas ignite.

Multiattack. The cerberus makes three bite attacks.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) piercing damage plus 2 (1d4) fire damage.