Chuul Nodemind

Amphibious. The chuul can breathe air and water.

Mental Feedback. While the chuul is conscious, it and all other chuul within 500ft are immune to psychic damage and cannot be charmed or frightened.  Furthermore, any creature which targets this chuul with an effect which would deal psychic damage or apply the charmed or frightened must make a DC14 Wisdom saving throw or take 13 (3d8) psychic damage, or half damage with a success.

Psychic Defense. The chuul adds its Wisdom Modifier to its armor class.  (Included in profile.)

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.

Innate Spellcasting (Psionics). The chuul’s innate spellcasting ability is Wisdom (spell save DC 14). The chuul can innately cast the following spells, requiring no components:

At will:  catapult, mage hand (the hand is invisible)

3/day each: counterspell, see invisibility, shield, 

1/day each: nondetection (Self and all Chuul within 500ft),phantasmal killer

Multiattack. The chuul makes two pincer attacks. If the chuul is grappling a creature, the chuul can also use its tentacles once.

Pincer. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage. The target is grappled (escape DC 14) if it is a Large or smaller creature and the chuul doesn't have two other creatures grappled.

Tentacles. One creature grappled by the chuul must succeed on a DC 14 Constitution saving throw 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.