
If the target is a Huge or larger nonmagical object or creation of magical force, this ray disintegrates a 10-foot cube of it. If the target is a Large or smaller nonmagical object or creation of magical force, it is disintegrated without a saving throw. If this damage reduces the creature to 0 hit points, its body becomes a pile offine gray dust. If the target is a creature, it must succeed on a DC 14 Dexterity saving throw or take 45 (10d8) force damage. The targeted creature must make a DC 14 Constitution saving throw, taking 36 (8d8) necrotic damage on a failed save, or half as much damage on a successful one. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. The targeted creature must succeed on a DC 14 Wisdom saving throw or be frightened for 1 minute. The targeted creature must succeed on a DC 14 Constitution saving throw or be paralyzed for 1 minute. The zombie uses a random magical eye ray, choosing a target that it can see within 60 feet of it. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. On a success, the zombie drops to 1 hit point instead. 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.

So to turn a zombie into a skeleton you'll need to kill it, strip its flesh off, pile the bones, then cast Animate Dead on it. Languages understands Deep Speech and Undercommon but can’t speak Zombies have bones, but given how the rules phrase it you'll need to have a pile of bones to make a skeleton rather than pulling them out of a creature.

On a specific success, the zombie could drop to 1 hit point instead of this. Senses darkvision 60 ft., passive Perception 9 Undead Fortitude: In any situation if the damage of Zombie Monster has reduced to 0 hit points and then it must make constitution saving throw by a DC of 5 + the damage has taken and then unless until the damage is radiant or from the critical hit.
