Undead

Undead (アンデッド) are creatures of the dead that have come back to the land of the living after death. They can be found in both YGGDRASIL and the New World.

Background
In YGGDRASIL, undead was one of the many races a Player can choose to be and play as. Moreover, such race is divided into different subspecies according to their racial level, allowing players to further evolve beyond it. This goes along well with the right classes like necromancer specifically that are befitting for someone who was an undead.

As an Overlord of a high-tier race, one could create a more powerful undead than what an Elder Lich or other undead are capable of doing. To create a permanent undead that cannot disappear easily until killed in battle, one needs the target's dead body or any least bit of their remains including bones to carry it out. The corpse's quality determines the level of an undead one creates. In this case, the Sunlight Scripture's corpses at most can create the kind of undead up to level 40 at max. Beyond such limit while using their corpses, the undead would vanish with the passage of time, along with the corpses that served as their medium. Even without a vessel for summoning the undead, he is still able to spawn one out of thin air. Yet the undead created also could not stay in the New World for long.

Moreover, the quality of the undead produced can vary by what kind of species the corpse originated from. In particular, dragons and trolls are among the corpses out there that could become a zombie or a skeleton. For humans, Ainz seems to use a human corpse as catalyst to keep his summoned Death Knight, a mid-tier undead or below permanent in the New World. There are even some among the Dragon Lords, one of the strongest species from the New World that were said to be an undead. Zesshi Zetsumei stated that both Elder Coffin Dragon Lord and Vampiric Dragon are presumed to be alive due to their race as undead while Captain of the Black Scripture thought they are already dead.

In some shape or form, Ainz's way of using the corpses seem as if a resurrection is taking place, yet the targets that are dead will come back to life as an undead rather than alive in the flesh through a racial skill. Ainz noted that without an intact corpse, there is a chance that if he used resurrection magic, it might become one of the undead. Though it is different from a normal resurrection via a tier spell, where the person is supposed to be brought back to life not as an undead, but part of the living instead. It seems also apparent that certain undead monsters have some sort of ability which allows them to spawn a weaker undead through the target they've killed. Depending on the undead, abilities like Crypt Lord or Overlord, they could go as far as buffed their own undead minions to be more stronger than it normally was supposed to be while controlling them.

In the Web Novel, soldiers who died without their weapons turn into undead, were equipped with different types of weapons. The most convincing argument among people was that the weapons were the representation of their will, possibly due to the interference of magic as some believed to be the cause.

Along the way, there happens to be a healing-type spell such as "Greater Lethal" that can heal the undead through it's generated Negative Energy. However, when exposed to the kind of healing-type spell that uses Positive Energy, undead can end up being the one who sustains the damage instead of the heal. As long as the negative energy which served to be their life-force was not depleted, the undead would keep on fighting. If the conditions for instant death were not met, they would not lose the will to fight like the living would. In that regard, the undead were perfect soldiers on the battlefield since they don't suffer from exhaustion or pain.

On the other hand, the undead are looked upon as monsters that possess an undying hatred for all living creatures and its intent was to eradicate them. The undead were viewed to be the enemy of all living beings negatively. Yet, there are few exceptions to this idea in which Ainz Ooal Gown, who doesn't see it the same way they do, but was still indifferent to them nonetheless in terms of not being able to show emotions physically. Despite Yuri Alpha being an undead, she doesn't seem to bear any ill hatred towards the living and regarded some of them with kindness instead. Also, the same could be said with Evileye, an undead who works in a group like Blue Roses consisting of humans.

Although the undead possesses hatred against the living, there are some like Davernoch who were able to somehow suppress it. He was considered to be a naturally-spawned Elder Lich capable of intelligence, going as far as forming a goal in life that includes harnessing the power of magic and learning techniques beyond the spells he could use since his genesis. In other words, certain sentient undead are capable of keeping their hatred under control when negotiating and forming relations with the living. If the living were the ones who try to offer negotiation first, then it would usually end up turning out to be a bad trade. But if the undead were to initiate the first offer or negotiation, there had once been instances of people obtaining ancient items that had been made with now-forgotten knowledge. Whenever Ainz issues mental commands over the weaker undead, they won't be able to easily attack the living out of their nature unless it was ordered to do so by their master.

While so, the undead do not age nor suffered from fatigue like the living go through. Hence, the undead would continue ruling the land for all eternity until it was defeated. Unlike the dragons' own growth rate, high-level undead are not the type to grow in bodily might. Instead, they could accumulate knowledge and experience constantly over time. From that point of view, the undead might be even stronger than dragons. Among the many undead out there, Titus, a Skeleton Mage is attempting to master a new methodology of crafting scrolls as well as translate the New World's language and thereby improve himself. In the New World, it seems there are legendary tales recorded and passed down about the undead such as an Astral Ripper or Wriggle Pestilence.

When a group of weaker undead gather in one place, stronger undead are then created after a certain period of time passes by. Undead normally spawned in places such as the Katze Plains or E-Rantel's graveyard where many people died. For example, a Death Knight and other undead spawning at that location tends to be a hotspot for their birth. Such effect could also be used in tangent alongside a magic ritual called Death Spiral that turn a living person into an undead like the Elder Lich. Though this ceremony requires the sacrifice of a location composed with living entities to form another place for naturally spawn undead. They gather together in numbers, causing the birth of a more powerful undead to appear one after another while the cycle continuously repeats itself.

Although the undead could be dominated through magic, the only human who succeeded in doing so was one of the Thirteen Heroes being Rigrit, a necromancer. However, dominating the undead requires a rather complicated process even for the likes of Fluder to master. The undead do also happen to have absolute resistance to the effect of mind control spells. Controlling the minds of undead with magic is next to impossible unless it was done through a World Item such as Downfall of Castle and Country. The control and destruction of undead should be done by priests using the power of the 'gods'. If one chooses to become an undead in the New World, their heart and mind will begin to alter as well. The change to the undead state often affects the soul too as far as Evileye knows it, since she is an example of one who was once a human being.

Basic Undead Race Traits

 * Bludgeoning Vulnerability V
 * Biological Penalties' Resistance
 * Critical Hit Immunity
 * Dark Vision
 * Death Immunity
 * Disease Immunity
 * Doubled Damage by Fire
 * Eating, Drinking, and Breathing are Unnecessary
 * Energy Drain Immunity
 * Good, Light and Holy Vulnerability IV
 * Good and Holy Consecrated Areas' Vulnerability II
 * Mind-affecting Immunity
 * Necromancy Resistance
 * Paralysis Immunity
 * Physical Penalty Resistance
 * Poisoning Immunity
 * Recover by Negative Energy
 * Sleep Immunity

Skeleton

 * Bone Vulture
 * Elder Lich
 * Nazarick Elder Guarder
 * Nazarick Master Guarder
 * Nazarick Old Guarder
 * Overlord
 * Skeletal Dragon
 * Skeleton Archer
 * Skeleton Centipede
 * Skeleton Mage
 * Skeleton Rider
 * Skeleton Warrior
 * Soul Eater

Zombie

 * Blood Meat Hulk
 * Corpse Collector
 * Death Knight
 * Dullahan
 * Eyeball Corpse
 * Freezing Zombie
 * Frost Bone
 * Ghast
 * Ghoul
 * Jack the Ripper
 * Necrosome Giant
 * Organ Egg
 * Plague Bomber
 * Squire Zombie
 * Undead Beast
 * Zombie Dragon
 * Zombie Troll

Death Spirit

 * Astral Ripper
 * Carrion Baby
 * Grim Reaper Thanatos
 * Ghost
 * High Wraith
 * Pale Rider
 * Screaming Banshee
 * Wight
 * Wraith

Vampire

 * Elder Vampire Bat
 * Lesser Vampire
 * True Vampire
 * Vampire Bat Swarm
 * Vampire Bride
 * Vampire Wolf

Unknown Undead

 * Corrupt Dead
 * Crypt Lord
 * Death Cavalier
 * Death Emperor
 * Death Empress
 * Elder Coffin Dragon Lord
 * Eternal Death
 * Greater Graveyard
 * Guphandera Argoros
 * Overlord Cronos Master
 * Overlord General
 * Overlord Wiseman
 * Swell Skin
 * Undead Lieutenant
 * Vampiric Dragon Lord
 * Wriggle Pestilence

Trivia

 * The Baharuth Empire is conducting experiments to make undead laborers under their control. However, it seems apparent that Ainz is already doing just that with his undead minions, lending them out to the citizens and dealers of his nation for various tasks.
 * Those who died a violent death and the dead who were not properly revered have the highest chance of becoming undead.
 * Because it is uncertain what causes the spontaneous genesis of the undead, the Baharuth Empire is currently investigating the reason for that.
 * To prevent the dead from becoming undead, the people of the New World have taken to making proper burials for the dead as soon as possible when death occurs.
 * Albedo once tried to conduct an experiment to determine which type of undead could feel emotions, but her findings were cut short after she got into an altercation with Shalltear.
 * There exists a secret society that only consisted of undead Magic Casters.
 * Undead were the first of its kind in the Overlord series known to spawn in the New World as it seem apparent that their birth looks to be limitless even after death.
 * Ainz plans to conduct an experiment on whether or not the soul was actually the cause for mid-tier undead like Soul Eaters to stay permanent in the New World rather than the corpse itself.
 * According to Osk, the undead are supposed to have poor physical stats, but that does not seem to be the case with Ainz.
 * Decapitation was quite a common one for most low tier undead beings.