Vampiric Warforged Mind Flayer

Quirk. Due to the Vampiric Warforged Mind Flayer’s (V.W.M.F) warforged heritage, they develop a quirk. They don’t understand emotions and often misread emotional cues. (The DM can ignore this quirk, however, and replace it with a roll on the Warforged quirk table).

Warforged and Mind Flayer Resilience. The V.W.M.F. have advantage on saving throws against being poisoned, and have resistance to poison damage. They are immune to disease. They don’t need to eat, drink, or breathe. They don’t need to sleep and don’t suffer the effects of exhaustion  due to lack of rest, and magic can’t put you to sleep. Lastly, they have advantage on saving throws against spells and other magical effects.

Innate Spellcasting (Psionics). The V.W.M.F.'s innate spellcasting ability is Intelligence (spell save DC 15). It can innately cast the following spells, requiring no components:
At will: detect thoughts, levitate
1/day each: dominate monster, plane shift (self only)

The Shapechange. If the V.W.M.F. isn't in sunlight or running water, it can use its action to polymorph into a Tiny bat or a Medium cloud of mist, or back into its true form.

While in bat form, the V.W.M.F. can't speak, its walking speed is 5 feet, and it has a flying speed of 30 feet. Its statistics, other than its size and speed, are unchanged. Anything it is wearing transforms with it, but nothing it is carrying does. It reverts to its true form if it dies.

While in mist form, the V.W.M.F. can't take any actions, speak, or manipulate objects. It is weightless, has a flying speed of 20 feet, can hover, and can enter a hostile creature's space and stop there. In addition, if air can pass through a space, the mist can do so without squeezing, and it can’t pass through water. It has advantage on Strength, Dexterity, and Constitution saving throws, and it is immune to all nonmagical damage, except the damage it takes from sunlight.

Legendary Resistance (3/Day). If the V.W.M.F. fails a saving throw, it can choose to succeed instead.

A Misty Escape. When V.W.M.F. drops to 0 hit points outside its resting place, the V.W.M.F. transforms into a cloud of mist (as in the Shapechanger trait) instead of falling unconscious, provided that it isn't in sunlight or running water. If it can't transform, it is destroyed.

While it has 0 hit points in mist form, it can't revert to its base form, and it must reach its resting place within 2 hours or be destroyed. Once in its resting place, it reverts to its base form. It is then paralyzed until it regains at least 1 hit point. After spending 1 hour in its resting place with 0 hit points, it regains 1 hit point.

False Flesh Regeneration. This creature regains 20 hit points at the start of its turn if it has at least 1 hit point and isn't in sunlight or running water. If the creature takes radiant damage or damage from holy water, this trait doesn't function at the start of its next turn.

Effortless Climbing. This creature can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Sentry’s Rest. When V.W.M.F. take a long rest, they must spend at least six hours in an inactive, motionless state, rather than sleeping. In this state, they appear inert, but are not rendered unconscious, and can see and hear as normal.

Weaknesses. The V.W.M.F. has the following flaws:

Forbiddance. They can't enter a residence without an invitation from one of the occupants.

Running Water Vulnerability. They take 20 acid damage if it ends its turn in running water.

Stake to the Core. If a piercing weapon made of wood is driven into the V.W.M.F.’s equivalent of a heart while the creature is incapacitated in its resting place, they are paralyzed until the stake is removed or if they die from other means.

Sunlight Sensitivity. The V.W.M.F. takes 15 radiant damage when it starts its turn in sunlight. While in sunlight, it has disadvantage on attack rolls and ability checks.

Multiattack (Base Form Only). The Vampiric Warforged Mind Flayer can make two attacks: either one or two unarmed or tentacle strikes, and/or a single bite or brain extraction attack - however, the bite or brain extraction can only be done once per turn and only if the conditions of the attacks are satisfied.

Unarmed or Tentacle Strike (Base Form Only). Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 15 (2dl0 + 4) bludgeoning or psychic (depending on which limb hits) damage. If the target is Medium or smaller, it is grappled (escape DC 18) and must succeed on a DC 18 Intelligence saving throw or be stunned until this grapple ends.

Brain Extraction or Bite. (Bat form can only bite - both can be used in Base Form). Melee Weapon Attack: +9 to hit, reach 5 ft., one willing creature, or a creature that is grappled by the V.W.M.F., incapacitated, or restrained.  Bite Hit: 7 (1d6 + 4) piercing damage plus 10 (3d6) necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the V.W.M.F. regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. A humanoid slain in this way and then buried in the ground rises the following night as a vampire spawn under the vampire's control. Brain Extraction Hit: 55 (10d10) piercing damage. If this damage reduces the target to 0 hit points, the V.W.M.F. kills the target by extracting and devouring its brain.

Mind Blast (Base Form Only——Recharge 5-6). The V.W.M.F. magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 17 Intelligence saving throw or take 22 (4d8 + 4) psychic damage and be stunned 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.

Charm. The V.W.M.F. targets one humanoid it can see within 30 feet of it. If the target can see the V.W.M.F., the target must succeed on a DC 17 Wisdom saving throw against this magic or be charmed by the vampire. The charmed target regards the vampire as a trusted friend to be heeded and protected. Although the target isn't under the  V.W.M.F.'s control, it takes the  V.W.M.F.'s requests or actions in the most favorable way it can, and it is a willing target for the  V.W.M.F.'s bite or brain extraction attack.

Each time the  V.W.M.F. or the  V.W.M.F.’s companions do anything harmful to the target, it can repeat the saving throw, ending the effect on itself on a success. Otherwise, the effect lasts 24 hours or until the  V.W.M.F. is destroyed, is on a different plane of existence than the target, or takes a bonus action to end the effect.

 Night Children (1/Day). The  V.W.M.F. magically calls 2d4 swarms of bats or rats (swarm of bats, swarm of rats) or squid (if underwater), provided that the sun isn't up. While outdoors, the  V.W.M.F. can call 3d6 wolves (wolf) instead. The called creatures arrive in 1d4 rounds, acting as allies of the  V.W.M.F. and obeying its spoken commands. The beasts remain for 1 hour, until the  V.W.M.F. dies, or until the  V.W.M.F. dismisses them as a bonus action.

The V.W.M.F. can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. This creature regains spent legendary actions at the start of its turn.

Move. The creature moves up to its speed without provoking opportunity attacks.

Unarmed or Tentacle Strike. The creature makes an unarmed strike.

Bite or Brain Extraction.(Costs 2 Actions). The creature makes one bite or Brain Extraction attack.