Bonehulk

Disassembly. When the bonehulk dies, it can spawn 7 (2d6) skeletons in an unoccupied spot within 10 feet of its location.

False Appearance. While motionless, the bonehulk is indistinguishable from a pile of bones.

Life Sense. The bonehulk can pinpoint the location of a living creature within 120 feet of it.

Necrotic Fortitude. The bonehulk's hit point maximum cannot be reduced in any manner. Whenever the bonehulk takes necrotic damage, it can recover a number of hit points equal to the damage taken.

Siege Monster. The bonehulk can deal double damage to buildings and objects.

Turn Resistance. The bonehulk has advantage on saving throws against effects that would turn undead.

Undead Fortitude.  If damage reduces the bonehulk to 0 hit points, it must make a Constitution saving throw with a DC equal to half the damage taken (minimum 10), unless the damage is radiant or from a critical hit. On a success, the bonehulk drops to 1 hit point instead.

Multiattack. The bonehulk can make two attacks with its skeleton spike.

Skeleton Spike. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 29 (4d10 + 7) bludgeoning damage.

Skeletal Greatspike. Ranged Weapon Attack: +11 to hit, range 120/240 ft., one target. Hit: 51 (8d10 + 7) piercing damage. Upon a hit, the target must succeed a DC 19 Strength saving throw. On a failed save, the target is restrained until it uses an action to free itself (escape DC 19).