Ancient Zombie Dragon

Turn Resistance. The zombie dragon has advantage on saving throws against any effect that turns Undead.

Undead Fortitude. If damage reduces the zombie dragon 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 zombie dragon drops to 1 hit point instead.

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

Multiattack. The zombie dragon can use its Frightful Presence. It then makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 32 (4d10 + 10) piercing damage.

Claw. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 24 (4d6 + 10) slashing damage.

Baleful Breath (Recharge 5–6). The zombie dragon exhales pestilent gas in a 90-foot cone. Each creature in that area must make a DC 23 Constitution saving throw, taking 66 (12d10) necrotic damage on a failed save, or half as much damage on a successful one.

Frightful Presence. Each creature of the zombie dragon's choice that is within 120 feet of the zombie dragon and aware of it must succeed on a DC 17 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the zombie dragon's Frightful Presence for the next 24 hours.