Cathulhu

Psychic Link Cathulhu can hear the thoughts of every creature within 60 feet of it

Spellcasting Cathulhu is a 9th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 8, +5 to hit with spell attacks). The [monster name] has following [class name] spells prepared:
Cantrips (at will): Message, Mind Sliver
1st level (2 slots): Dissonant Whispers, Cause Fear                                                                    5th level (2 slots): Dominate Person

Induce Madness Force a creature within 20 feet of you tto make a Wisdom saving throw, DC 13. On a failed save, the target must attack the nearest creature friendly to it. At the end of each of their turns, they can make the same save to end this state.

Demonic Claw Melee Attack: +2 to hit, range of 5 ft., 1 target. Hit: 2d4 Slashing damage.

Psychic Burst Ranged Spell Attack: +5 to hit, range 20/60 ft., 2 targets. Hit: 1d8 + 3 Psychic damage.

Shatter Mind If a creature is still affected by Drive to Insanity or Induce Madness, it takes 2d6 Psychic damage

Drive to Insanity The creature that most recently attacked Cathulhu must attack a creature within 5 feet of it. If there are multiple creatures next to it, the creature attacks the one with the highest initiative.

Cathulhu gets one legendary action per round. Legendary action can happen at any point, including during another creature's turn

Demonic Flight Cathulhu can change from Walking to Flying without expending any movement

Cathulhu can take one Mythic action on its turn

Tentacle Strike Target creature you can see is Restrained for 2 turns