Adult Black Dragon Zombie

Legendary Resistance (3/Dayr). If the zombie dragon fails a saving throw, it can choose to succeed instead.

Undead Fortitude. If damage reduces the zombie to 0 Hit Points, it makes a Constitution saving throw with a DC equal to 5 plus the damage taken, unless the damage is Radiant or from a Critical Hit. On a successful save, the zombie drops to 1 Hit Point instead.

Multiattack. The zombie makes three Rend attacks. It can replace one attack with a use of Corpse Bile.

Rend. Melee Attack Roll: +11, reach 10 ft. Hit: 13 (2d6 + 6) Slashing damage plus 4 (1d8) Acid damage.

Corpse Bile. Dexterity Saving Throw: DC 18, one creature the zombie dragon can see within 60 feet. Failure:  (12d8) Acid damage. Success: Half damage.

Grave Miasma (Recharge 5–6). Constitution Saving Throw: DC 18, each creature in a 60-foot Cone. Failure: 45 (10d8) Necrotic damage, and the target has the Poisoned condition and can’t regain Hit Points until the end of its next turn. Success: Half damage only.

Legendary Action Uses: 3 . Immediately after another creature's turn , the dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each its turns.

Cloud of Insects. Dexterity Saving Throw: DC 17, one creature the dragon can see within 120 feet. Failure: 22 (4d10) Poison damage, and the target has Disadvantage on saving throws to maintain Concentration until the end of its next turn. Failure or Success: The dragon can’t take this action again until the start of its next turn.

Horrifying Groan. Wisdom Saving Throw: DC 17, each creature of the zombie dragons’s choice within 30 feet that can hear it. Failure: The target has the Frightened condition until the end of its next turn. Failure or Success: The zombie can’t take this action again until the start of its next turn.

Pounce. The dragon can move up to half its Speed, and it makes one Rend attack.