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 zombie drops to 1 hit point instead.

This saving throw succeeds automatically the first time the Zombie Dragon drops to 0 hit points.

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

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) piercing damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

Breath Weapons (Recharge 5–6). The dragon uses one of the following breath weapons.

Necrotic Breath. The dragon exhales fire in a 40-foot line that is 5 feet wide. Each creature in that line must make a DC 14 Dexterity saving throw, taking 42 (12d6) necrotic damage on a failed save, or half as much damage on a successful one.

Sleep Breath. The dragon exhales sleep gas in a 30-foot cone. Each creature in that area must succeed on a DC 14 Constitution saving throw or fall unconscious for 5 minutes. This effect ends for a creature if the creature takes damage or someone uses an action to wake it.