Multiattack. The yaggol uses Extract Brain or Mind Blast once, and makes one Tentacle or Psychic Bolt attack.

Tentacles. Melee Attack Roll: +5, reach 10 ft. Hit: 6 (1d6 + 3) Psychic damage, and if the target is Large or smaller, it is Grappled (escape DC 13).

Psychic Bolt. Ranged Attack Roll: +4, range 80/320 ft. Hit: 11 (2d8 + 2) Psychic damage.

Extract Brain. Intelligence Saving Throw: DC 11, one creature within 30 feet of the yaggol. Failure: 11 (2d10) Psychic damage, and until the target finishes a Long Rest or dies, its Proficiency Bonus is cumulatively lowered by 1. The yaggol gains a cumulative +2 bonus to damage rolls. A creature whose Proficiency Bonus drops to 0 can’t form new thoughts or speak, and it has Disadvantage on attack rolls and d20 Tests. Success: Half damage, and the target's Proficiency Bonus is not reduced. Failure or Success: If this damage reduces the target to 0 Hit Points, the yaggol kills it and devours its brain.

Mind Blast (1/Day). Intelligence Saving Throw: DC 14, each creature in a 15-foot cone. Failure: 14 (4d6) Psychic damage. Success: Half damage.

Weaken Will. Trigger: A creature Grappled by the yaggol makes a saving throw against one of the yaggol's powers. Response: The creature has Disadvantage on the saving throw.