Controller

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

Psionic Aura. When a creature starts or ends its turn within 10 ft of the controller they take 2d10 psychic damage and must succeed a DC 18 Intelligence saving throw or become stunned until beginning of the creatures next turn 

Innate Spellcasting (Psionics). The controller's innate spellcasting ability is Intelligence (spell save DC 18). It can innately cast the following spells, requiring no components::
At Will: dominate monster
1/day each: Suggestion, Geas, Synaptic Static

Psionic Blast. Melee Attack +8 to hit, range 5ft., single target. Hit: 8 (1d6+5) 

Psionic Bolt. Ranged Attack: +8 to hit, range 240 ft., single target. Hit: 13 (2d8 + 5) psychic damage. If the target is hit by 4 they take an extra 1d8

Mind Blast (Recharge 5-6). The controller magically emits psychic energy. Creatures of the controller choice within 60 feet of it must succeed on a DC 18 Intelligence saving throw or take 32 (5d10 + 5) psychic damage and be stunned for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

The controller can take 3 legendary actions, choosing from the options below. It can take only one legendary action at a time and only at the end of another creature’s turn. The elder brain regains spent legendary actions at the start of its turn.

• Break Concentration. (1 Action) The controller targets a creature within 120 feet of it with which it has a psychic link. The controller breaks the creature’s concentration on a spell it has cast. The creature also takes 1d4 psychic damage per level of the spell.