Cerberus Guardian

Keen Hearing and Smell. The guardian has advantage on Wisdom (Perception) checks that rely on hearing or smell. The cerberus can pinpoint, by scent, the location of any soul within 30 feet of it.

Multiple Heads. The guardian has three heads. While it has more than one head, the Cerberus has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.  Whenever the guardian takes 56 or more damage in a single turn, one of its heads dies. If all its heads die, the guardian dies.

Cerberus' Curse. Whenever Cerberus hits a creature with its bite attack, that creature is forced to remain in its current plane until the curse is removed by the remove curse spell or other magic.  While under this curse, the guardian knows the distance and direction of the cursed creature. 

 Heated Body. An enemy that touches the monster or hits it with a melee attack while within 5 ft of it takes  (1d10 + 2) fire damage

Multiple Attacks.  Each round, the Guardian makes a number of bite attacks corresponding to the number of heads remaining, against either a single target or multiple targets standing adjacent to each other.  It will also make one claw attack. 

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 10 (3d6 + 3) piercing damage.  A creature successfully bitten will be subject to the Cerebos' curse. 

Claw.  Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 3) slashing damage, and an additional 18 (4d6 + 3) fire damage.  If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone.  The Guardian will step over the creature knocked prone, where it will do additional damage with its Heated Body.  

Breath Weapon (Recharge 5–6). One of Cerberus' heads will exhale a 15-foot cone of molten rock. Each creature in the cone must make a DC 14 Dexterity saving throw, taking 10 (3d6) fire damage on a failed save, or half as much damage on a successful one. On a failed save, a creature is also restrained by the hardening rock. A creature can make a DC 14 Strength (athletics) check as an action, freeing itself or a creature within reach from the rock on a success. The rock has AC 17 and 10 hit points, and it is immune to fire, poison, and psychic damage.

Consume Flesh.  At the end of an enemy's turn, the Guardian can take a legendary action.  It will consume the flesh of a recently killed creature, healing itself for 3d6+8 points.