Cerberus, The Gatekeeper V. 2

Three Headed. Each head has a mind of it's own. This allows Cerberus to either use his bite attack, fire breath or noxious fume attack once per round for each head available. Cerberus has advantage on perception checks based on sight, hearing and smell. Additionally, he is immune to charming effects because of his three separate minds.

Life Consumption. Cerberus has the passive ability to consume the life force of creatures near him. Whenever a healing spell is cast on a target within 15 ft. of Cerberus, he heals half of the amount the intended target was healed for. 

Multiattack. Cerberus makes three bite attacks, uses his Fire Breath or his Noxious Fumes (once per head per turn).

Bite. Melee Weapon Attack: +9 to hit, reach 5 ft., single target. Hit: 16 (2d10 + 4) Piercing damage and 2d4 Fire damage. If Cerberus hits a target with this attack, he may attempt to grapple that target (Large creatures and smaller). Target must succeed an Athletics check DC 19 or be grappled. While grappled, the head cannot make any attacks at another creature, but can repeat the bite attack at the grappled target with advantage.

Fire Breath (Recharge 5-6). 30 ft. cone. Targets within the effected area must succeed on a Dexterity saving throw DC 17 or take 8d6 Fire damge, or half as much on a success. If there are any targets grappled by the heads of Cerberus, they automatically fail the save and take the full damage.

Noxious Fumes (Recharge 1-2). 15 ft. cone. Targets within the effected area must succeed on a Constitution save DC 17 or take 6d6 Poison Damage, or half as much on a success. Those who fail will be poisoned until the end of their next turn.

Death Glare (2 times per day). Single target. Range: 60 ft. Cerberus stares into the very soul of a creature. The target must succeed on a Charisma save DC 16 or take 6d6 Psychic damage. If the creature succeeds the save, there is no affect.

Opportunity Attack. Because Cerberus has 3 individual heads, he can take the opportunity attack reaction three times per round, but not all three against the same creature at once.

Cerberus can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Cerberus gains spent legendary actions at the start of his next turn.

Soul Expulsion (Costs 2 Actions). Cerberus leaps to a target area, up to 45 ft away. Upon landing, creatures within 15 ft must make a Constitution saving throw DC 17 or take 3d6 necrotic damage. Cerberus heals for half the amount of total damage dealt this way.

Paralyzing Spit (Costs 1 Action). +7 to hit, 1d6 to 4d6 acid damage. As Cerberus attacks successfully throughout the encounter, his heads begin to awaken. If no heads are awake, the attack is made only by the tail. If all heads are awake, the target must succeed a Constitution saving throw DC 16 or be stunned until the end of Cerberus's next turn.

Stygian Torment (Costs 2 Actions). Cerberus jumps slightly straight into the air and crashes down and a wave of necrotic and psychic energy surrounds him. All creatures within 30 ft must succeed on a Constitution saving throw or take 5d8 necrotic damage, half as much on a successful save. After the damage is dealt, Cerberus then lifts all targets who failed the save and places them 15 ft in front of his heads. Those who succeed the initial save are not affected by this.