Bone Coalescence

Siege Monster. The Bone Coalescence deals double damage to structures.

Necrotic Absorption. If the Bone Coalescence is hit by an effect that would deal Necrotic Damage it instead regains a number of temporary hit points equal to the damage it would have been dealt.

Shield of Shadows. While the Bone Coalescence has temporary hit points it is covered in a murky, shadowy veil that allows it to be treated as if it were in complete darkness for the purpose of having resistance to piercing, bludgeoning and slashing damage.

Shadow Backlash. If the Bone Coalescence takes damage that would reduce it's temporary hit points by any source, each creature within 5 ft of the Bone Coalescence must make a DC 18 Constitution Saving Throw or take an amount of damage equal to the initial amount of Temporary HP the Bone Coalescence had before it took the damage just applied in Necrotic Damage and taking half of that damage on a success.

Multiattack. The Bone Coalescence can make two Slam attacks, either Slam Attack can be replaced with one Hurl Bone attack. If the Bone Coalescence has a creature grappled it may use Assimilate instead of a Slam attack.

Slam. Melee Weapon Attack: +9 to hit, reach 15 ft., 1 target. Hit: 22 (3d10 + 5) Bludgeoning damage. If the target is a creature, it is grappled (Escape DC 18). Until this grapple ends, the target is restrained. The Bone Coalescence can have up to two creatures grappled this way at once, one for each arm.

Hurl Bone. Ranged Weapon Attack: +9 to hit, range 20/60 ft., 1 target. Hit: # (2d12 + 5) Piercing damage.

Assimilate. The Bone Coalescence makes one Slam attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the Slam's damage, the target is thrust into the chest of the Bone Coalescence, and the grapple ends. While being Assimilated, the creature is Incapacitated, it has total cover against attacks and other effects outside the Bone Coalescence, and it takes 22 (4d10) necrotic damage, 11 (2d10) piercing damage, gains 1 level of Exhaustion, and permanently loses 1 Strength, 1 Dexterity and 1 Constitution at the start of each of the Bone Coalescence's turns. Any Stat Drain that a creature receives is added to the total of the Bone Coalescence's overall stats. If a creature drops to zero hit points or any of their ability scores drop to zero while being assimilated the Bone Coalescence gains 30 Temporary Hit Points, the creature being assimilated dies instantly and can only be revived by means of a wish spell. The Bone Coalescence can only attempt to assimilate one creature at a time.

If the Bone Coalescence takes 40 damage or more on a single turn, the Bone Coalescence must succeed on a DC 18 Constitution saving throw at the end of that turn or lose the creature currently being assimilated, which fall prone in a space within 10 feet of the Bone Coalescence. If the Bone Coalescence dies, a creature in the process of being assimilated remains entrapped until freed by another creature or by passing a DC 15 Athletics Check, taking 1d10 Piercing Damage on a failed check.