Cerebrax

Legendary Resistance (3/day). If Cerebrax fails a saving throw, it can choose to succeed instead.

Innate Spellcasting (Psionics). Cerebrax's innate spellcasting ability is Intelligence (spell save DC 18, +10 to hit with spell attacks). It can innately cast the following
spells, requiring no material components:

At will: levitate, detect thoughts, psionic hand (mage hand)
1/day each: teleport (self only), hold monster, mental prison, dominate monster, feeblemind

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

Tactics: When he was of sound mind, Cerebrax could form unbelievably complex strategies and lead armies of encephalids in battle. Now, in his mentally diminished state, he just lashes against any potential threat to him or to the Repository he is still trying to access. He doesn't hold back but instead uses excessive amounts of force even against smaller threats. If he realizes that his opponents are close together he uses his deadly psychic blast and his powerful psionic abilities to crush them all together. He doesn't fear or maybe he doesn't realize his imminent death so he will fight
until the end.

Multiattack. Cerebrax can use its Frightful Presence. It then makes three attacks: one with its tentacles and two with its claws.

Tentacles. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 28 (4d10+ 6) bludgeoning damage plus 5 (1d10) psychic damage.If the target is huge or smaller, it is
grappled (escape DC 20) and must succeed on a DC 18 Intelligence saving throw or be stunned until this grapple ends.

Claw. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 19 (3d8 + 6) slashing damage.

Tail Tentacle. Melee Weapon Attack: +12 to hit, reach 20 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage. If the target is huge 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.

Feed on Brains. Melee Weapon Attack: +12 to hit, reach 10 ft., one incapacitated intelligent creature grappled by the Cerebrax. Hit: The target takes 33 (6d10) piercing damage and 4 points of Intelligence damage. If this damage reduces the target to 0 hit points or the target's Intelligence score to 0, Cerebrax kills the target by reducing the target's brain into a pulp. Intelligent damage can be removed by restoration spells.

Psychic Blast (Recharge 5-6). Cerebrax magically emits psychic energy in a 60 ft. cone. Each creature in that area must succeed on a DC 18 Intelligence saving throw or take
45 (10d8) 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.
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 16 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.

Reaction Name. Enter the description for your action.

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. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail tentacle attack.

Wing Attack (Costs 2 Actions). Cerebrax beats his wings. Each creature within 15 ft. of him must succeed on a DC 20 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning
damage and be knocked prone. Cerebrax can then fly up to half its flying speed.

Ride the Brainwaves (Costs 3 Actions). Cerebrax's form quivers and disappears with a sucking noise. Cerebrax reappears in an empty space beside an intelligent (4 or higher) creature he can see.