Coelenite Mass Mind (CFTD)

Colony Resistance. The coelenite has advantage on saving throws against spells and magical effects that target only it.

Colony Weakness. If the coelenite has half its hit points or fewer it’s Intelligence score drops to 5 (-3), it can’t use it’s Innate Spellcasting, Limited Telepathy, or Psychic Crush.

Innate Spellcasting (Psionics). The coelenite’s innate spellcasting ability is Intelligence (spell save DC 12). It can innately cast the following spells, requiring no material
components:
At will: shape water
3/day each: jump, create or destroy water
1/day each: hold person, phantasmal force

Limited Amphibiousness. The coelenite can breathe air and water, but it needs to be submerged at least once every 4 hours to avoid suffcoating.

Limited Telepathy. The coelenite can magically transmit simple messages and images to any creature within 60 feet of it that can understands a language. This form of telepathy doesn’t allow the receiving creature to telepathically respond unless that creature is a coelenite.

Melee Attack. Claw Attack: +5 to hit, reach 5 ft., 1 target. Hit: 13 (3d6 + 3) bludgeoning damage, or 6 (1d6 + 3) bludgeoning damage if the swarm has half its hit points or fewer. A target hit by the attack is grappled (escape DC 15). The coelenite has two claws, each of which can grapple one target.

Psychic Crush (Recharge 5-6). The coelenite targets one creature that it can sense within 60 feet of it. The target must make a DC 12 Intelligence saving throw, taking 10 (3d6) psychic damage on a failed save, or half as much damage on a successful one.