The elder brain is aware of the presence of creatures within 3 mile of it that have an Intelligence score of 6 or higher. It knows the distance and direction to each creature. as well as each one’s intelligence score, but can’t sense anything else about it. A creature protected by a mind blank spell. a nondetection spell, or similar magic can’t be perceived in this manner.

A perfect being gets a +4 to intelligence and +2 to both wisdom and charisma

The elder brain’s innate spellcasting ability is Intelligence, 

It can innately cast the following spells, requiring no components:

• At will: detect thoughts, levitate

• 1/day each: dominate monster, plane shift (self only)

he elder brain can use its telepathy to initiate and maintain telepathic conversations with up to seven creatures at a time. The elder brain can let those creatures telepathically hear each other while connected in this way.

Melee Weapon Attack: +4 to hit, reach 15 ft., one target. Hit: 10 (2d8+2) bludgeoning damage. If the target is a large or smaller creature, it is grappled (escape DC 10) and takes 6 (1d8+2) psychic damage at the start of each of its turns until the grapple ends. The elder brain can have up to two targets grappled at a time.

The elder brain magically emits psychic energy. Creatures of the elder brain’s choice within 30 feet of it must succeed on a DC 14 Intelligence saving throw or take 18 (3d10+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 elder brain targets one incapacitated creature it can perceive with its Creature Sense trait and establishes a psychic link with that creature. Until the psychic link ends, the elder brain can perceive everything the target senses. The target becomes aware that something is linked to its mind once it is no longer incapacitated, and the elder brain can terminate the link at any time (no action required). The target can use an action on its turn to attempt to break the psychic link, doing so with a successful DC 14 Charisma saving throw. On a successful save, the target takes 6 (2d6) psychic damage. The psychic link also ends if the target and the elder brain are more than 1 mile apart, with no consequences to the target. The elder brain can form psychic links with up to five creatures at a time.

The elder brain targets a creature with which it has a psychic link. The elder brain gains insight into the target’s reasoning, its emotional state, and thoughts that loom large in its mind (including things the target worries about, loves, or hates). The elder brain can also make a Charisma (Deception) check with advantage to deceive the target’s mind into thinking it believes one idea or feels a particular emotion. The target contests this attempt with a Wisdom (Insight) check. If the elder brain succeeds, the mind believes the deception for 1 hour or until evidence of the lie is presented to the target.

blindsight 60 ft.

You can understand Undercommon and deep speech, you cannot speak but you use telepathy

Your unarmored AC is 10 + your Int modifier. You cannot wear armor but you still can attune to armor getting their bonuses. (you can only be attuned to 3 items at once)