Black Flame Ghost

Desolate Aura. At the start of each of the black flame ghost's turns, each creature within 5 feet of it takes 12 (2d12) fire damage, and flammable objects in the aura that aren't being worn or carried ignite. A creature that touches the black flame ghost or hits it with a melee attack while within 5 feet of it takes 12 (2d12) fire damage.
At the end of the black flame ghost's turns, it takes 1d6 + X psychic damage, where X is the number of Turns it's been active.

Desolate Form. The black flame ghost can move through a space as narrow as 1 inch wide without squeezing.

Death Throes. When the black flame ghost dies, it explodes, and each creature within 30 feet of it must make a DC 19 Dexterity saving throw, taking 24 (4d12) fire damage on a failed save, or half as much damage on a successful one. The explosion ignites flammable objects in that area that aren't being worn or carried.

Life Theft. If the black flame ghost damages a living creature, it heals itself for half the damage it dealt, with the exception of its Death Throes ability. If it kills a living creature, it restores health equal to Xd8 where X equals the total hit dice of the killed creature.

Multiattack. The black flame ghost can attack twice with its Claws

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 9 (1d6 + 6) slashing damage plus 4 (1d8) fire damage.

Cry for Life (Recharge 5~6). All creatures within a 10 foot radius of the black flame ghost must make a DC 19 Wisdom Saving Throw. On a fail, they take 10 (3d6) points of Psychic damage and are frightened of the black flame ghost until the end of their next turn.

Paradoxical Soul. If a spell targets the mind, soul, or lifeforce of a black flame ghost, then the user takes Xd8 points of Psychic Damage, where X is the level of the spell cast and the black flame ghost has advantage on any saving throws required.