Vantholoth

Innate Spellcasting. The vantholoth's innate spellcasting ability is Charisma (spell save DC 16). The vantholoth can innately cast the following spells, requiring no material components:

2/day each: hold person, dispel magic, speak with dead, shadow blade (3rd level)

1/day: spirit shroud ( alternatively: spirit guardians )

1/day: sickening radiance

Magic Resistance. The vantholoth has advantage on saving throws against spells and other magical effects.

Canopic Containment. If the vantholoth reduces a creature to 0 hit points using it's Spirit-Chain Spear, the creature dies and it's soul is captured in one of the vantholoth's canopic jars as if by a soul cage spell. While inside, the creatures soul is aware of its surroundings but cant say or do anything unless prompted by the vantholoth. The vantholoth carries 1d8 canopic jars with them, 1d4 of which are already full. 

Query Soul.  The vantholoth asks one of the souls it carries a question (no action required) and receives a brief telepathic answer, which it can understand regardless of the language used. The soul knows only what it knew in life, but it must answer truthfully and to the best of its ability. The answer is no more than a sentence or two and might be cryptic.

Magic Weapons. The vantholoth's weapon attacks are magical.

Multiattack. The vantholoth makes two attacks: one with its Torch and one with its Spear. 

A Flame to Light Your Way. As an action the vantholoth ignites it's torch. When a non-fiend creature that can see the vantholoth's torch starts its turn within 30 feet of it and does not avert their gaze, they must make a DC 15 Wisdom saving throw. If the saving throw fails by less than 5, it takes 16 (3d10) psychic damage.
If the saving throw fails by 5 or more, it is charmed by the vantholoth. Additionally, if the creature that failed had more than 20 hit points, it is reduced to 20 hit points. A creature charmed in this way cannot speak, make attacks, or cast spells, and will follow the vantholoth, using up to its full movement and its action to dash on its turn. 
 If a creature takes damage, they may reroll the saving throw, breaking the charm on a success. The charm is also broken if a charmed creature starts it's turn more than 100 ft. from the vantholoth, or if the vantholoth douses it's torch.  

Soulmonger's Torch. Melee Weapon attack: +7 to hit, range 5 ft., one target. Hit: 8 (1d6+4) bludgeoning damage, and if it is ignited: 12 (2d10) necrotic damage. While lit, the aura of the vantholoth's torch deals 2 necrotic damage to any creature that ends its turn within 30 feet of it. Undead and fiend's ignore this effect.

Spirit-Chain Spear. Ranged Weapon Attack: +7 to hit, range 50/200 ft., one target. Hit: 19 (3d10 + 4) force damage, and the target is grappled (escape DC 15) as this ephemeral spear reforms into a chain between the target's soul and the vantholoth. While grappled in this way, a creature’s speed isn’t reduced, but it can move only in directions that bring it closer to the vantholoth. A creature cannot break this grapple using Strength or Dexterity based checks, but can using Wisdom or Charisma based ones. A creature takes 5 (1d10) force damage if it escapes from the grapple or if it tries and fails. If the creature is undead, they have disadvantage on checks made to break the grapple and vulnerability to the attack's damage. 

The vantholoth can grapple up to 3 creatures at a time with this action, after which it cannot make attacks with the spear. This action ignores immunity to grapple. 

Eyes of the Dead. The vantholoth names a place where any one of the souls it is carrying saw in life, which creates an invisible sensor somewhere in that place if it is on the plane of existence it is currently on. The sensor remains for as long as the vantholoth concentrates, up to 10 minutes (as if it were concentrating on a spell). It receives visual and auditory information from the sensor as if it were in its space using it's senses.

A creature that can see the sensor (such as one using see invisibility or truesight) sees a translucent image of the tormented humanoid whose soul was caged.

Teleport. The vantholoth magically teleports, along with any equipment it is wearing or carrying, up to 60 feet to an unoccupied space it can see.

Borrow Experience. The vantholoth can use a bonus action to bolster itself with a soul’s life experience, making it's next attack roll, ability check, or saving throw with advantage. If it doesn’t use this benefit before the start of it's next turn, it is lost.

Steal Life. The vantholoth can use a bonus action to drain vigor from one soul and regain 2d8 hit points. It can do this as many times as it has trapped souls per day and only once per soul. 

Reel In. As a bonus action, the vantholoth can pull a creature grappled by it 20 feet closer.