Cerberus

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

Multiple Heads. The cerberus has three heads. While it has more than one head, the cerberus has advantage on saving throws against being blinded, charmed, deafened, stunned, and 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.

Relentless Tracker. The cerberus knows the distance to and direction of any creature under the effect of its curse, as long as the creature and the cerberus are on the same plane of existence. If the creature being tracked by the cerberus dies, the cerberus knows.

Soul Scent. The cerberus can pinpoint, by scent, the location of any soul within 30 feet of it.

Multiattack. The cerberus makes as many bite attacks as it has heads.

Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 11 (1d8 + 7) piercing damage plus 10 (3d6) fire damage. If the target is a creature, the creature is cursed and cannot leave the plane it is currently on until the curse is removed by the remove curse spell or other magic.

Howl (2/Day). Cerberus lets out a horrifying howl. Each creature that can hear it within 60 feet must make a DC 15 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. A frightened creature has disadvantage on this save, and takes 4d6 psychic damage on a failed save instead.

Fire Breath (Recharge 4-6). The cerberus exhales fire in a 15-foot cone. Each creature in the area must make a DC 17 Dexterity saving throw, taking 35 (10d6) fire damage on a failed save, or half as much damage on a successful one.

Take Down. Cerberus makes a claw attack.

Charge. If its speed isn't 0, Orthrus moves up to 10 feet without provoking opportunity attacks. If it makes an attack immediately after this movement, it has advantage on that attack.