Aspect of the Moon: The Shah doesn't need to sleep, and can't be forced to sleep by any means.
Pact Magic (14th-level, Cha-based, +7 hit, DC 15).
--At will: Mage Armor, Levitate, Silent Image, Eldritch Blast (add Cha to damage), Friends, Mage Hand, Minor Illusion, Vicious Mockery, Toll the Dead, Shape Water
--Rituals: Alarm, Purify Food and Drink, Water Breathing, Phantom Steed
--5th-level (3 slots): Witch Bolt, Dissonant Whispers, Charm Person, Mind Spike, Phantasmal Force, Detect Thoughts, Enemies Abound, Hex, Hold Person, Synaptic Static, Dominate Person, Mirror Image
Create Thrall: The Shah touches an incapacitated humanoid, infecting it with Melancholy's alien magic. That creature is Charmed by the Shah until a Remove Curse effect is cast, or the Charmed condition ends. As long as they are on the same plane of existence, the Shah can telepathically communicate with the target.
Dagger: +6 hit, 1d4+3 piercing damage.
Enslaved: This villager is enslaved by Melancholy the aboleth. It is under Melancholy's control, can't take reactions, and is in constant telepathic communication with the aboleth. Whenever the villager takes damage, it can make a DC 14 Wis save. On a success, it breaks free of Melancholy's control and returns to its own faculties.
Scimitar: +4 hit, 1d6+2 slashing damage.
Shapechanger (true form: halfling).
Amphibious (hybrid form only).
Multiattack: In halfling form, the deep scion makes two longsword attacks. In hybrid form, the deep scion makes one bite attack and two claw attacks.
Longsword: +6 hit, 1d10+4 slashing damage.
Bite: +6 hit, 1d4+4 piercing damage.
Claw: +6 hit, 1d6+4 slashing damage.
Psychic Screech (recharges on a short or long rest): The deep scion emits a terrible scream audible within 300 feet. Creatures within 30 feet of the deep scion must make a DC 13 Wis save or be stunned until the end of the scion's next turn. In water, the psychic screech also telepathically transmits the deep scion's memories of the last 24 hours to Melancholy the aboleth, regardless of distance, so long as both of them are in the same body of water.
Limited Amphibiousness: The sea spawn can breathe air and water, but needs to be submerged in the Oasis of Tears at least once a day for 1 minute to avoid suffocating.
Multiattack: The sea spawn makes to unarmed strikes and one tentacle attack.
Unarmed Strike: +4 hit, 1d4+2 bludgeoning damage.
Tentacle: +5 hit, reach 10 ft., 1d6+2 bludgeoning damage, and if the target is a Medium or smaller creature it is grappled (escape DC 12). Until the grapple ends, the sea spawn can't use its tentacle on another target.
Sense Magic: The chuul senses magic within 120 feet of it at will. This trait otherwise works like the Detect Magic spell but isn't itself magical.
Multiattack: the chuul makes two pincer attacks. If the chuul is grappling a creature, it can also use its tentacles once.
Pincer: +6 hit, reach 10 ft., 2d6+4 bludgeoning damage, and the target is grappled if it is a Large or smaller creature (escape DC 14). The chuul can only grapple two creatures at a time.
Tentacles: One creature grappled by the chuul must succeed on a DC 13 Con save or be Poisoned for 1 minute. Until this poison ends, the target is paralyzed. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Mucous Cloud: Any creature who touches or lands a melee attack against the aboleth while it is underwater and within 5 feet of it must make a DC 14 Con save. On a failure, the creature is diseased for 1d4 hours. The diseased creature can breathe only underwater.
Probing Telepathy: If a creature communicates telepathically with Melancholy, the aboleth learns the creature's greatest desires of it can see the creature.
Multiattack: Melancholy makes three tentacle attacks.
Tentacle: +9 hit, reach 10 ft., 2d6+5 bludgeoning damage and the target must mae a DC 14 Con save. On a failed save, the creature is diseased. For 1 minute, the disease has no effect and can be removed by any disease-curing magic. After 1 minute, the creature's skin becomes translucent and slimy, and it can't regain hit points unless it is underwater. At this stage, the disease can only be removed by Heal or other disease-curing magic of 6th-level or higher. The diseased creature takes 1d12 acid damage every 10 minutes it is not in contact with water.
Tail: +9 hit, reach 10 ft., 3d6+5 bludgeoning damage.
Enslave (3/Day): 30 foot visual range, one creature must make a DC 14 Wis save or be Charmed by Melancholy until they are on different planes of existence or Melancholy dies. The Charmed target is under Melancholy's control, can't take reactions, and is in constant telepathic communication with Melancholy. The target can repeat the save whenever it takes damage or spends a day more than 1 mile away from Melancholy.
Detect: Melancholy makes a Perception check.
Tail Swipe: Melancholy makes a tail attack.
Psychic Drain (Costs 2 actions): One creature charmed by Melancholy takes 3d6 psychic damage, and Melancholy regains hit points equal to the damage the creature takes.