Talk:Zombie Dragon/@comment-190.246.39.207-20180719145026/@comment-45.56.46.26-20180720084739

Well, basic undead immunities like "critical hits, mind-affecting, poison, disease, sleep, paralysis, death and energy drain effects. Resistance to necromancy and biological penalties. Undead did not need to breathe, eat or drink. They were healed by negative energy and had darkvision."

But Ainz can create them using one of his skills or abilities (most likely undead creation) as long as he has a suitable (meaning dragon) corpse handy. Skeletal Dragons seem to require a spell. So there's no real reason for them to be comparable.