Multiattack

The malleable makes three flesh tendril attacks.

Flesh Tendril

Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 20 (4d6 + 6) bludgeoning damage. If the target is a Huge or smaller creature, it is grappled (escape DC 16).

Psychic Drain

One creature grappled by the malleable must make a DC 16 Intelligence saving throw, taking 45 (10d8) psychic damage on a failed save, or half as much damage on a successful one. The target's hp maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies and becomes a minor malleable if this effect reduces its hp maximum to 0.

Join Malleables

As long as the malleable is within 10 feet of one other major malleable, both malleables can use this action option at the same time to join together to create a massive malleable. The new malleable's hp total is equal to the combined hp total of both major malleables, and it is affected by any conditions, spells, and other magical effects currently affecting either of the major malleables. The new malleable acts on the same initiative count as the malleables that formed it and occupies any unoccupied space that previously contained at least one of the malleables that formed it.

Separate Malleables

The major malleable can split into eight minor malleables or two moderate malleables. The new malleables' hp totals are equal to the major malleable's hp total divided by the number of malleables created (rounded down) and are affected by any conditions, spells, and other magical effects that affected the major malleable. The new malleables act on the same initiative count as the major malleable and occupy any unoccupied space that previously contained the major malleable.