Advanced Telepathy. The Flumph Cloister can perceive the content of any telepathic communication used within 100 feet of it, and it can't be surprised.

Telepathic Shroud. The Flumph Cloister is immune to any effect that would sense its emotions or read it's thoughts, as well as divination spells.

Group Sport. Each hit point that the Flumph Cloister has is equivalent to one Flumph. A Flumph Cloister can grow if any Flumphs join it, increasing its maximum hit points by the number of Flumphs join it. Any single target attacks that don't harm any surrounding targets deal a maximum of one damage to the Flumph Cloister. Alternatively, any Area of Effect attacks deals the maximum amount of damage.

Multiattack. The Flumph Cloister can make 2 tendril attacks, one of which can be replaced with a flumph shot.

Tendril. Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 31 (10d4 + 6) acid damage. At the end of each of its turns, the target must make a DC 15 Constitution, taking 7 (5d4) acid damage on a failure or ending the recurring acid damage on a success. A lesser restoration spell cast on the target also ends the recurring acid damage.

Flumph Shot. The Flumph Cloister can sacrifice hit points to fire off Flumphs at several creatures. It can use up to 20 of its hit points, 2 per Flumph, to make an attack roll (+10 to hit). Each Flumph deals 2d4 bludgeoning and die on impact.

Stench Spray (Recharge 5-6). Each creature in a 60-foot cone originating from the Flumph Cloister must succeed on a DC 15 Dexterity saving throws or be coated in a foul-smelling liquid. A coated creature is poisoned as long as the stench lasts, and other creatures are poisoned within 5 feet of the coated creature. A creature can only remove the stench on itself by using a short rest to bathe in water, alcohol, or vinegar.

Split. The Flumph Cloister can give disadvantage to a creature targeting it with a single target attack.

The Flumph Cloister has 2 legendary actions, which they can only use on other creature's turns and they regain them at the start of their turn.

Tendrils. Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 31 (10d4 + 6) acid damage. At the end of each of its turns, the target must make a DC 15 Constitution, taking 7 (5d4) acid damage on a failure or ending the recurring acid damage on a success. A lesser restoration spell cast on the target also ends the recurring acid damage.

Flumph Shot. The Flumph Cloister can sacrifice hit points to fire off Flumphs at several creatures. It can use up to 20 of its hit points, 2 per Flumph, to make an attack roll (+10 to hit). Each Flumph deals 1d4 bludgeoning and die on impact.