Behelder Brain

Antimagic Sphere. The Behelder Brain creates an area of antimagic, as in the antimagic field spell, in a 60-foot-sphere centered on itself. At the start of each of its turns, the Behelder Brain decides whether the sphere is active. The area works against the Behelder Brain's own eye rays.

     While the sphere is active, the Behelder Brain acts as though affected by the incapacitated condition and its speed is 0. While in this state, the Behelder Brain regains 22 4d10 Hit Points at the end of its turn. 

Innate Spellcasting. The Behelder Brain's innate spellcasting ability is Intelligence (spell save DC 20). The Behelder Brain can innately cast the following spells, without providing material components:

At will: Detect Thoughts, Misty Step

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

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

Psychic Touch. When the Behelder Brain is hit with a melee attack, the attacker's mind is invaded with whispers from the Behelder Brain's many minds, and takes 2 (1d4) psychic damage. This cannot be reduced in any way.

Telepathic Hub. The Behelder Brain hears whispers of the thoughts of any creature within a mile of it, and it can use its telepathy to initiate and maintain telepathic conversations with up to ten willing creatures at a time. The Behelder Brain can let those creatures telepathically hear each other while connected in this way.

Tentacle. Melee Weapon Attack: +10 to hit, reach 30 ft., one target. Hit: 14 (4d6) bludgeoning damage. If the target is Huge or smaller, it is grappled (escape DC 18) and and takes 15 (2d8 + 6) psychic damage at the start of each of its turns until the grapple ends. The Behelder Brain can have up to four targets grappled at a time.

Bite (Hover only). Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 14 (4d6) piercing damage and 14 (4d6) psychic damage.

Mind Blast (Recharge 5-6). The Behelder Brain magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 20 Intelligence saving throw or take 39 (7d10) 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.

Eye Rays (Hover only). The Behelder Brain shoots three of the following magical eye rays at random (reroll duplicates), choosing one to three targets it can see within range. +10 to hit, reach 120 ft., one target. A creature cannot be targeted by multiple Eye Rays at one time.

1. Charm Ray. The targeted creature must succeed on a DC 18 Wisdom saving throw or be charmed by the Behelder Brain for 1 hour, or until the Behelder Brain harms the creature.
2. Paralyzing Ray. The targeted creature must succeed on a DC 18 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
3. Banishing Ray. The targeted creature must succeed on a DC 18 Charisma saving throw or be banished for 1 minute, as in the banishment spell. The target can repeat the saving throw at the end of each of its turns, ending the effect on a success. If the spell ends before 1 minute has passed, the target reappears in the space it left or in the nearest unoccupied space if that space is occupied. Otherwise, the target doesn't return without other magical means.
4. Slowing Ray. The targeted creature must succeed on a DC 18 Constitution saving throw. On a failed save, the target’s speed is halved for 1 minute. In addition, the creature can’t take reactions, and it can take either an action or a bonus action on its turn, not both. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
5. Imprisoning Ray. The target must succeed on a DC 18 Intelligence saving throw or suffer the effects of the mental prison spell (Look it up). Regardless whether the target succeeds or fails, they take 27 (5d10) psychic damage. 
6. Telekinetic Ray. If the target is a creature, it must succeed on a DC 18 Constitution saving throw or the Behelder Brain moves it up to 30 feet in any direction. It is restrained by the ray’s telekinetic grip until the start of the Behelder Brain’s next turn or until the Behelder Brain is incapacitated.
   If the target is an object weighing 300 pounds or less that isn’t being worn or carried, it is moved up to 30 feet in any direction. The Behelder Brain can also exert fine control on objects with this ray, such as manipulating a simple tool or opening a door or a container.
7. Sleep Ray. The targeted creature must succeed on a DC 18 Wisdom saving throw or fall asleep and remain unconscious for 1 minute. The target awakens if it takes damage or another creature takes an action to wake it. This ray has no effect on constructs and undead.
8. Enfeebling Ray. The targeted creature takes 14 (4d6) psychic damage and must make a DC 18 Intelligence saving throw.  On a failure, the creature becomes feebleminded, as in the feeblemind spell. The creature's Intelligence and Charisma scores become 1. The creature can't cast spells, activate magic items, understand language, or communicate in any intelligible way. The creature can, however, identify its friends, follow them, and even protect them.
9. Disintegration Ray. If the target is a creature, it must succeed on a DC 18 Constitution saving throw or take 45 (10d8) force damage. If this damage reduces the creature to 0 hit points, its body becomes a pile of fine gray dust.
   If the target is a Large or smaller nonmagical object or creation of magical force, it is disintegrated without a saving throw. If the target is a Huge or larger object or creation of magical force, this ray disintegrates a 10-foot cube of it.
10. Death Ray. The targeted creature must succeed on a DC 18 Constitution saving throw or take 55 (10d10) necrotic damage. The target dies if the ray reduces it to 0 hit points.

When the Behelder Brain is encountered for the first time, it will be Dormant, sitting motionless in large pool of psychic fluids to keep itself and its brains moisturized, effectively incapacitated. Because the creature is vain and believes itself to be the most superior being in existence, it will remain motionless until its protective crust has been damaged.

The Behelder Brain can take 2 legendary actions, using the options below. It can take only one legendary action at a time and only at the end of another creature’s turn. The Behelder Brain regains spent legendary actions at the start of its turn.

Regeneration. The Behelder Brain regains 11 (2d10) Hit Points.

When the Behelder Brain's hit points drops to zero for the first time while in its Dormant state, it regains all lost hit points and becomes Awakened. The outer crust cracks and falls apart as the Behelder Brain slowly hovers out of the pool.

The Behelder Brain can take 4 mythic actions, using the options below. It can take only one mythic action at a time and only at the end of another creature’s turn. The Behelder Brain regains spent mythic actions at the start of its turn. The Behelder Brain cannot use a mythic action at the same time as a legendary action.

Eye Ray. The Behelder Brain uses one random eye ray.

Misty Step. The Behelder Brain casts the Misty Step spell and can make one Tentacle or Bite Attack.

Break Concentration (Costs 3 Actions). The Behelder Brain targets a creature within 120 feet of it with which it has a psychic link. The Behelder Brain breaks the creature's concentration on a spell it has cast. The target also takes 1d6 psychic damage per level of the spell.