Brainstealer Dragon

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

Innate Spellcasting (Psionics). The brainstealer dragon’s innate spellcasting ability is Intelligence (spell save DC 15). It can innately cast the following spells, requiring no components:

At will: detect thoughts

1/day each: plane shift (self and rider only)

Psionic flight. The brainstealer dragon has levitate cast on it at all times

Void Dweller. Brainstealer dragons dwell in the empty expanse between the stars, and do not require air, food, drink, or sleep. When flying between stars the brainstealer dragon magically glides on solar winds, making the immense journey through the void in an impossibly short time.

Psionic Patron. The brainstealer dragon bonds with a creature 

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its tentacle and two with its claws. It can replace its tentacle attack with extract brain.

Tentacles. Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 15 (2d10 + 4) psychic damage plus 7 (2d6) bludgeoning. 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: +7 to hit, reach 5 ft., one incapacitated humanoid grappled by the brainstealer dragon. Hit: The target takes 55 (10d10) piercing damage. If this damage reduces the target to 0 hit points, the brainstealer dragon kills the target by extracting and devouring its brain or it can form its psionic bond.

Claw. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Tail. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 18 Wisdom saving throw or become frightened 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. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Mind Blast (Recharge 5–6). The dragon explodes psyonic  energy in a 30-foot radius. Each creature in that area must make a DC 15 Intelligence saving throw, taking 63 (12d6) Psychic damage damage on a failed save and be stunned for 1 minute or half as much damage on a successful one.

They may make another save at the end of the round.

Psionic Bond (1/day). The brainstealer dragon casts dominate person. When the dragon casts it in this way it doesn't require concentration and is dominated until the dragons next long rest. The Dragon can use its mind blast through its patron

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

Detect Thought. The dragon casts detect thoughts.

Tail Attack. The dragon makes a tail attack.

Tentacle Attack. The dragon makes a tentacle attack.

Tentacle Leap (Costs 2 Actions). Using its tentacles, the brainstealer moves up to 40 feet to an unoccupied space adjacent to a wall, ceiling, floor, or other solid surface. This move doesn’t trigger reactions. The brainstealer must have at least one tentacle free (not grappling a creature) to use this action. Grappled creatures move with the brainstealer