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

Legendary Resistance (3/Day). If the vampiric illithid fails a saving throw, it can choose to succeed instead.

Misty Escape. When it drops to 0 hit points outside its resting place, the vampiric illithid 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 vampiric form, and it must reach its resting place within 2 hours or be destroyed. Once in its resting place, it reverts to its vampiric 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.

Regeneration. The vampiric illithid 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 it takes radiant damage or damage from holy water, this trait doesn't function at the start of its next turn.

Spider Climb. The vampiric illithid can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Vampire Weaknesses. The vampiric illithid has the following flaws:

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

Harmed by Running Water. The vampiric illithid takes 20 acid damage if it ends its turn in running water.

Stake to the Heart. If a piercing weapon made of wood is driven into the vampiric illithid's heart while the vampiric illithid is incapacitated in its resting place, it is paralyzed until the stake is removed.

Sunlight Hypersensitivity. The vampiric illithid takes 20 radiant damage when it starts its turn in sunlight. While in sunlight, it has disadvantage on attack rolls and ability checks.

Photosensitive Fury.  The vampiric illithid despises light from any source. If a creature holds a light, such as a torch or an object affected by the light spell at the start of vampiric illithid's turn, the vampiric illithid must attack that creature at least once on its turn. If it doesn’t, it has disadvantage on attacks against other creatures.

Sanguine Tentacles. Melee Weapon Attack: +8 to hit, reach 5 ft., one creature. Hit: 15 (2d10 + 4) psychic damage plus 11 (2d10) necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the vampiric regains hit points equal to that amount. The reduction lasts until the target finishes a long rest.

If the target is Medium or smaller, it is grappled (escape DC 15) and must succeed on a DC 15 Intelligence saving throw or be stunned until this grapple ends.

Extract Brain. Melee Weapon Attack: +8 to hit, reach 5 ft., one incapacitated humanoid grappled by the vampiric illithid. Hit: The target takes 55 (10d10) piercing damage. If this damage reduces the target to 0 hit points, the vampiric illithid kills the target by extracting and devouring its brain.

Mind Blast (Recharge 5–6). The vampiric illithid magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 16 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.

The vampiric illithid 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. The vampiric illithid regains spent legendary actions at the start of its turn.

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

Sanguine Tentacle (Costs 2 Actions). The vampiric illithid makes one sanguine tentacle attack.

Extract Brain. (Costs 3 Actions). The vampiric illithid makes an extract brain attack.