Undead Dragon Torso

Unusual Nature. The undead dragon torso doesn't require air, food, drink, or sleep.

Turn Resistance. The undead dragon torso has advantage on saving throws made against effects that turn undead.

 Undead Fortitude. When the undead dragon torso drops to 0 HP, it instead drops to 1 hp, unless it the damage was caused by a critical hit or was radiant damage.

Multiattack. The undead dragon torso makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 14 (2d8 + 5) piercing damage plus 4 (1d8) necrotic damage.

Claw. Melee Weapon Attack: +9 to hit, reach 5 ft. one target. Hit: 8 (1d6 + 5) slashing damage. If the target is a Medium or smaller creature, it is grappled (escape DC 15). Until this grapple ends, the target is restrained. The dragon has two claws, each of which can grapple one target.

Cataclysmic Breath (Recharge 5–6). The undead dragon torso exhales a wave of ghostly purple flames in a 30-foot cone. Each creature in that area must make a DC 16 Dexterity saving throw, taking 36 (8d8) necrotic damage on a failed save, or half as much damage on a successful one. A creature dies if the breath reduces it to 0 hit points. 

The Undead Dragon Torso may take one Legendary Action at the end of another creature's turn. During that Legendary Action, it may make one Bite or Claw attack against a creature in its range. Alternatively, it may:

Ram. The undead dragon torso uses its great horns to punch forward, all creatures in a 15ft by 5ft-line directly in front of the undead dragon torso's face must succeed a DC 19 Dexterity saving throw or be knocked prone and take 4d4 bludgeoning damage, taking none on a successful save.