Zombified Hull. AC is increased or decreased depending on where specific ranged attacks or line spells are aimed. As a DM, make sure to share this with your players in order to let them know to specify where they aim.

Melee Attack. Claw Swipe: Damage 20, range 1ft

Action Ranged Attack. Fire Breath: Damage 30, range 10ft

Tail Parry. Any ranged attacks the dragon sees can be deflected if it chooses. However, it takes a Nat 20 (1d20) to do so, otherwise it is dealt 1 piercing damage.

A Zombie Dragon can use its legendary actions when it is damaged for more than 1/4 of its HP as a reaction.

Legend's End. This move targets all creatures that can see it, or it can see. If a character has the Folk Hero background, it instantly dies. Otherwise, deal 1d4*1/4 of the target's HP as the Zombie Dragon emanates a dark smell that even a rogue can sense is evil for it.

This creature can only use mythic actions when on 1 hp. Elsewise, its turn is skipped if it tries.

Mythic World's Rot. The Zombie Dragon emanates a foul smell, as its scales and hull rot. All creatures within the range of Infinity that are not obstructed by any objects are instantly obliterated. Its scales fall off, none to witness. It's still-beating heart and lungs show through its skeletal form as any Characters, dead or alive, within 30 meters are healed to full to witness the melting skeleton before them. Death is required for life.