Ancient Arcanist. Aboleths are undoubtedly skilled at domination and illusion, but veiled masters are the true experts of the arcane.

Veiled masters engineered the deceptions and manipulations of ancient humanity's culture.

Their hidden gifts and subtle coaxings did much to encourage humanity's first rise to glory in that age, and in many of those first empires, veiled masters walking among the populace, whispering into their leaders' ears.

The people knew the veiled masters as powerful wizards, and there were murmurs that the mysterious cabal was more than human, but few suspected the truth for very long. The veiled masters quelled such suspicions by doing violence to the bodies and minds of those who proved too curious.

When the veiled masters first learned of humanity's growing hubris--of their belief that they were greater than their patrons--these manipulators punished humanity. At first, the punishments were minor, yet to the veiled masters' surprise and frustration, they only strengthened humanity's resolve.

In the end, destruction was deemed the answer, and as human culture fell into ruins, the veiled masters retreated to the depths of the sea, content for now that the devastation above would serve as a lesson that would never be forgotten.

The average veiled master measures 14 feet in length and weighs 1,500 pounds.

Amphibious. The veiled master can breathe air and water.

Mucous Cloud.While underwater, the veiled master is surrounded by a transformative mucus. A creature that touches the veiled master or that hits it with a melee attack while within 5 feet of it must make a DC 20 Constitution saving throw. On a failure, the creature is diseased for 1d4 hours. The diseased creature can only breathe underwater.

Probing Telepathy.If a creature comminucates telepathically with the veiled master, the veiled master learns the creature's greatest desires and darkest fears if they can see the creature. Additionally, for each minute of continued telepathic communication, the veiled master can experience one of that creature's memories.

Innate Spellcasting.A veiled master's spell casting ability is Charisma (spell save DC 19). It can innately cast the following spells, requiring no material components:

At will: Glyph of Warding, Suggestion

3/day: Major Image, Symbol

1/day each: Polymorph (self only), Programmed Illusion, Teleport

Tentacle. Melee Weapon Attack: +9 to hit, 20ft. reach, one target. Hit: 13 (2d8+4) bludgeoning damage plus 21(6D6) lightning damage.

If the target is a creature, it must succeed on a DC 20 Constitution saving throw or become diseased. The disease has no effect for 1 minute and can be removed by any magic that cures disease. After 1 minute, the diseased creature's skin becomes translucent and slimy, the creature can't regain hit points unless it is underwater, and the disease can be removed only by Heal or any other disease-curing spell of 6th level or higher. When the creature is outside a body of water, it takes 6(1D12) acid damage every 10 minutes unless moisture is applied to the skin before 10 minutes have passed.

Bite. Melee Weapon Attack: +9 to hit, 10ft. reach, one target. Hit: 15 (2D10+4) piercing damage.

If the target is a creature, it must succeed on a DC 17 Wisdom saving throw or suffer an additional 27 (6D6+6) psychic damage as the veiled master consumes its memories. The target's hit point maximum is reduced by an amount equal to the psychic damage taken, and the veiled master regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. If the target's hit point maximum is reduced to 0, it remains alive and conscious and is treated as though it had 1 hit point, but it becomes a mindless slave of the veiled master, as though affected by the veiled master's enslave ability.

Enslave (3/day). The veiled master targets one creature it can see within 60 feet of it. The target must succeed a DC 19 Wisdom saving throw or be magically charmed by the veiled master until the veiled master dies or until it is on a different plane of existence from the target. The charmed target is under the veiled master's control and can't take reactions, and the veiled master and the target communicate telepathically with each other over any distance.

Whenever the charmed target takes damage, the target can repeat the saving throw. On a success, the effect ends. No more than once every 24 hours, the target can also repeat the saving throw when it is at least 1 mile away from the veiled master.

Action Melee Attack. Melee Weapon Attack: +# to hit, reach # ft., # target. Hit: # (#d# + #) [damage type] damage. 

Action Ranged Attack. RangedWeapon Attack: +# to hit, range #/# ft., # target. Hit: # (#d# + #) [damage type] damage.

The veiled master can take 4 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The veiled master regains spent legendary actions at the start of its turn.

Detect. The veiled master makes a Wisdom (Perception) check.

Mental Assault. The veiled master bombards the mind of a single creature within 60 feet with psychic static. That creature has disadvantage on all D20 rolls it makes until the beginning of its next turn.

Psychic Drain (costs 2 actions). One creature charmed by the veiled master takes 21 (6D6) psychic damage, and the veiled master regains hit points equal to the damage the creature takes.