Undead fortitude. If damage reduces the creature 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 creature drops to 1 hit point instead.

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack:  hit 15 (2d10+4) peircing and plus 4 (1d8) acid damage 

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

Tail. Melee Weapon Attack: up to 3 targets in a curve, 8 (2d4+4) bludgeoning damage. 

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 16 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 dragon's Frightful Presence for the next 24 hours.

Plagued Breath:  The creature spits out the zombie virus in breath wepoen form If any corpse or person with opened wounds gets touched by it they will be turned into  zombie under the dragons control a blessing and healing word will heal people currently alive while those who are dead cannot be turned back.

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 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.