Beholder of Ash

Legendary Resistance (3/Day, or 4/Day in Lair). If the beholder fails a saving throw, it can choose to succeed instead.

Multiattack. The beholder uses Eye Rays two times, or 1 Bite and a single eye ray.

Bite. Melee Attack Roll: +8, reach 5 ft. Hit: 13 (3d6 + 3) Piercing damage.

If consumed in this attack they must make 3 successful constitution Saving throws or become consumed in ash. Also if the beholder of ash uses bite on a ashed creature it is instantly consumed and the beholder recovers 2d10 health.

P.S. ash mephits will actively be consumed to sustain the beholder, and the cult leader will have a legendary action to throw himself into the beholder at low health.

Eye Rays. The beholder randomly shoots one of the following magical rays at a target it can see within 120 feet of itself (roll 1d10; reroll if the beholder has already used that ray during this turn):

1: Paralyzing Ray. Constitution Saving Throw: DC 16. Failure: The target has the Paralyzed condition and repeats the save at the end of each of its turns, ending the effect on itself on a success. After 1 minute, it succeeds automatically.
2: Fear Ray. Wisdom Saving Throw: DC 16. Failure: 14 (4d6) Psychic damage, and the target has the Frightened condition until the end of its next turn.
3: Slowing Ray. Constitution Saving Throw: DC 16. Failure: 18 (4d8) Necrotic damage. Until the end of the target’s next turn, the target’s Speed is halved; the target can’t take Reactions; and it can take either an action or a Bonus Action on its turn, not both. Success: Half damage only.
4: Enervation Ray. Constitution Saving Throw: DC 16. Failure: 13 (3d8) Poison damage, and the target has the Poisoned condition until the end of its next turn. While Poisoned, the target can’t regain Hit Points. Success: Half damage only.
5: Petrification Ray. Constitution Saving Throw: DC 16. First Failure: The target has the Restrained condition and repeats the save at the end of its next turn if it is still Restrained, ending the effect on itself on a success. Second Failure: The target has the Petrified condition instead of the Restrained condition.
6: Disintegration Ray. Dexterity Saving Throw: DC 16. Failure: 36 (8d8) Force damage. If the target is a nonmagical object or a creation of magical force, a 10- foot Cube of it disintegrates into dust. Success: Half damage. Failure or Success: If the target is a creature and this damage reduces it to 0 Hit Points, it disintegrates into dust.

Antimagic Cone. The beholder’s central eye emits an antimagic wave in a 150-foot Cone. Until the start of the beholder’s next turn, that area acts as an Antimagic Field spell, and that area works against the beholder’s own Eye Rays.

If no cone is in use it gets a reaction of counterspell, or dispell magic.

If Cone is not in use one use of either counterspell or dispell magic.

Legendary Action Uses: 3. Immediately after another creature’s turn, the beholder can expend a use to take one of the following actions. The beholder regains all expended uses at the start of each of its turns.

Chomp. The beholder makes two Bite attacks.

Glare. The beholder uses Eye Rays.

Become One With Ash. Beholder consumes the nearest creature to turn them to ash, and regain [roll]2d10[/roll]