Zarruthul

Multiattack. The drake makes three attacks, only one of which can be a Bite or Tentacle attack, and it can use Psychic Maelstrom if available.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 21 (3d10+4) piercing damage plus 14 (4d6) psychic damage.

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 15 (2d8+4) slashing damage.

Psychic Tentacle. Melee Weapon Attack: +10 to hit, reach 15 ft., one creature. Hit: 18 (2d10+4) bludgeoning damage, and the target is grappled (escape DC 18). While grappled, the drake can spend its action to siphon thoughts: the target takes 21 (6d6) psychic damage and must succeed on an Intelligence saving throw (DC 18) or be stunned until the end of the drake's next turn. A creature can be grappled by only one of the drake's tentacles at a time.

Mind Blast (Recharge 5-6). The drake emits a concussive psionic wave in a 60-foot cone. Each creature in that area must succeed on an Intelligence saving throw (DC 18) or take 45 (10d8) psychic damage and be stunned for 1 minute. A stunned creature can repeat the save at the end of each of its turns, ending the effect on a success.

Psychic Maelstrom (1/Day). Zarruthul unleashes a sustained psychic storm in a 30-foot-radius sphere centered on itself. For 1 minute, the area is filled with whispering, overlapping memories. Creatures that start their turn in the area or enter it for the first time on a turn must succeed on an Intelligence saving throw (DC 18) or take 27 (6d8) psychic damage and have their memories of the last 24 hours scrambled — they take a -4 penalty to Wisdom and Intelligence checks and saving throws while inside the area and for 1d4 hours after leaving. Each round the area persists, Zarruthul can choose one affected creature within the area to be charmed instead (Wisdom save ends, DC 18).

Reflective Mind. When Zarruthul would be targeted by a spell that forces an Intelligence, Wisdom, or Charisma save, it can use its reaction to gain advantage on the save. If the save succeeds, the spell is reflected back at the caster as if the caster had failed a save (the caster must make the appropriate save against the spell if required).

Detect. Zarruthul makes a Wisdom (Perception) check.

Tail Sweep. Melee Weapon Attack: +10 to hit, reach 20 ft., one target. Hit: 17 (2d8+4) bludgeoning damage and the target must succeed on a Strength saving throw (DC 18) or be knocked prone.

Mental Spike (Costs 2 Actions). One creature Zarruthul can see within 120 feet must succeed on an Intelligence saving throw (DC 18) or take 18 (4d8) psychic damage and have one memory flash outward as an illusory scene only others can perceive; this scene can distract (granting disadvantage on the target's next attack and on Wisdom checks for its allies who see it).

Dominate Echo (Costs 3 Actions). Zarruthul targets one creature it can see within 90 feet. The target must succeed on a Wisdom saving throw (DC 18) or be charmed for 1 minute, obeying Zarruthul's telepathic commands. The creature can repeat the save at the end of each of its turns. Only one creature can be affected by Dominate Echo at a time.