Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the Zombified Adult Black Dragon drops to 1 hit point instead.

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

Multiattack. The dragon can make three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 4 (1d8) acid damage.

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Tail. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.

Acid Breath (Recharge 5–6). The dragon exhales acid in a 60-­foot line that is 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 27 (6d8) acid damage on a failed save, or half as much damage on a successful one.

The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 16 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone.