Bone Amalgam

Unusual Nature. A Bone Amalgam doesn’t require air, drink, or sleep. 

Osseous Construct. Bone Amalgam are Constructs in addition to being Undead. They are the grim sum of any number of harvested skeletons, and typically sport specialized abilities and limbs representative of the services they were raised to render. Bone Amalgam are most commonly built bipedally with four clawed limbs, but can feature other limbs, features, or abilities representative of the corpses they are constructed of. Examples of specialized limbs are included as Bonus Actions.

Churning Bone. The Bone Amalgam is a writhing construct of regenerative bone. The Amalgam can set this bone mass to new and renewed purposes as needed. As a reaction the Amalgam may make use of its Boneforge ability at the following rate of conversion: 1 Bone Mass = 10hp = 1 Claw = 1 Leg = .5 Specialized Limb = .5 Head

Living Bone. The Bone Amalgam regains 10 hit points at the start of each of its turns.  If the Bone Amalgam takes radiant damage this trait doesn't function at the start of the Bone Amalgam's next turn. The Bone Amalgam dies only if it starts its turn with 0 hit points and doesn't regenerate.

Multiattack. The Bone Amalgam makes a Claw attack for each intact limb and can use either Repurpose Bone or Seize Skeletons, if available.

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) slashing damage plus 21 (6d6) necrotic damage.

Repurpose Bone. The Amalgam chooses a size Large or smaller Humanoid with 0 hit points that it can see within 30 feet of it. That creature is teleported inside the cavernous ribcage of the Amalgam and imprisoned there. While imprisoned in this way, the creature is restrained and has disadvantage on death saving throws. If the creature dies while imprisoned, the Amalgam regains 25 hit points and immediately recharges Seize Skeletons. Additionally, at the start of its next turn the Amalgam generates one new limb for each size category above Tiny of the slain creature, and the Amalgam regurgitates the slain creature's soft tissues as a bonus action. The regurgitated creature becomes a boneless. An Amalgam can imprison only one creature at a time.

Seize Skeletons (Recharge 6). The Amalgam reaches out tendrils of necromantic power and attempts to seize the skeletons of creatures in a 20-foot radius centered on itself. Each creature in that area must make a DC 18 Constitution saving throw, taking 44 (8d10) necrotic damage on a failed save, or half as much damage on a successful one. If a creature is reduced to 0 hit points in this way it dies as its bones are torn from its body to join the Amalgam, granting a free use of Repurpose Bone.

The following are examples of possible additions to a Bone Amalgam using its Osseous Construct feature, and should be considered Specialized Limbs for the purpose of its Ruinous Parry. 

Bonebreath (Recharge 5-6). An appended dragon skull exhales shards of entropic bone in a 60-foot line that is 5 feet wide. Each creature in that line must make a DC 18 Dexterity saving throw, taking 54 (12d8) necrotic damage on a failed save, or half as much damage on a successful one.

Mounted Gaze. The Amalgam stokes false life into Beholder skull appended to an articulated spine. The Amalgam may choose between triggering a Beholder's Antimagic Cone feature (lasting until the beginning of the Amalgam's next turn unless lost to Ruinous Parry) or else making its Eye Rays attack.

Boneforge. The Bone Amalgam may meld and recombine its bone mass into new shapes. The Amalgam may exchange any number of Claws and Legs, or may regrow a Head or Specialized Limb for its appropriate Bone Mass exchange (see Churning Bone).

Ruinous Parry. The Bone Amalgam may choose to sacrifice a part of its body to avoid the worst of an attack. The Bone Amalgam adds 6 to its AC as the sacrificial limb shatters into a cloud of bone dust. The Amalgam suffers a Bone Consequence conditional upon the lost limb. Bone Consequences stack, as the Amalgam shatters its own body in relentless commitment to its designed purpose.

• Claw - The Amalgam loses access to the limb for the purpose of its Multiattack.
• Leg - The Amalgam suffers a percent penalty to its base move speed (-50% of bipedal, -25% if quadrupedal, reaching 0 upon destruction of last leg).
• Specialized Limb - The Amalgam loses access to the ability granted by the limb.
• Head - The Amalgam is Blinded with respect to creatures Medium or smaller who are not wearing heavy armor, and loses the ability to distinguish between allies and foes on the battlefield.