Infected Elder Brain

The elder brain is aware of creatures within 1 mile of itself that have an Intelligence score of 4 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.

The elder brain has advantage on saving throws against spells and other magical effects.

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

The elder brain makes two Tentacle attacks.

Melee Attack Roll: +6 to hit, reach 30 ft., one target. Hit: 15 (3d8 + 2) bludgeoning damage. If the target is a Huge or smaller creature, it has the grappled condition (escape DC 14) and takes 9 (1d8 + 5) psychic damage at the start of each of its turns until the grapple ends. The elder brain can have up to four targets grappled at a time.

Creatures of the elder brain's choice within 60 feet of itself must succeed on a DC 17 Intelligence saving throw or take 32 (5d10 + 5) psychic damage and have the stunned condition for 1 minute. A stunned creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

The elder brain casts one of the following spells, requiring no spell components and using Intelligence as the spellcasting ability (spell save DC 17):

At will: detect thoughts, levitate