Summoner

Summoners refers to a general class of magic casters that exist in YGGDRASIL and the New World in Overlord. Not just simply a class name, but other individuals not belonging to the class can still be classify as one to some degree by summoning a monster of their own from other means elsewhere.

List of Summoning-oriented classes

 * Summoner
 * Necromancer

Overlord

 * Create High Tier Undead (4/day)
 * Create Middle Tier Undead (12/day)
 * Create Low Tier Undead (20/day)

List of Special Skills and Abilities

 * Unnamed Special Ability: It allows Kyouhukou to summon forth a myriad of cockroaches both large and small.
 * Breath of Fly: It allows Entoma to shoot forth a swarm of small flies. These flies then lay eggs in their victims. The maggots quickly hatch and eat the victim's flesh and rapidly grow to flies, only to repeat the process with new victims. This ability can only be used 3 times per day.
 * Unnamed Skill: It allows Ainz to create upper-tier undead four times a day. However, if he divided those up into two uses, he could make undead of roughly level 90. For starters, this special skill allows him to summon either the thief-type Eternal Deaths, or sensory-focused Eyeball types under his command.
 * Unnamed Skill: With her special skill, Shalltear can turn a low level undead she created into a lesser Vampire.

List of Summoning Spells and Magic
When a summon spell is already activated by its summoner, casting another summon spell would cause the previous summon spell to end abruptly. The currently-summoned monsters would go back from whence they came and new monsters would be summoned in their place. It is even possible for a summoner like Ainz to conjure forth monsters with a Super-Tier Spell.

Besides requiring mana, summoning spells can called forth monsters with different costs. For instance, the function of a Super-Tier Spell, Iä Shub-Niggurath is needed with a lot of people alive as sacrificial pawns in order to summon the Dark Youngs. Whereas the racial ability or tier spell to summon monsters weaker than that appear out of thin air freely without sacrifices. On the other hand, utilizing a dead body or body part meant that the summoned undead can stay in the New World without duration until one is killed in battle.

Additionally, a non-human summoner who specialized in summoning undead can also make use of their racial ability in tangent with dead bodies, serving to be a catalyst for other things. This includes not only Ainz making the undead permanent, but as well as for performing rituals to learn spells, and developing undead creation skills. Still, the strength of an undead created by Ainz is variably dependent on the quality of the dead corpses being used or else in an area filled with undead gathered together that is capable of spawning a stronger one.

Being a human necromancer, Khajiit utilizes an unknown ritual in the New World which requires sacrificing a city. It was the kind of sacrifices that needed people living in the city as a gateway for spawning undead endlessly. In other words, a city of living could later become a city of undead if this ritual is conducted successfully.

Tier Spells

 * Animate Dead: It allows the user to create a low level undead, but with his or her special skill, it can become a lesser Vampire.
 * Armageddon - Evil: A 10th tier spell that summon an army of demons. According to the standards of YGGDRASIL players, said demons are not considered to be strong. Moreover, other demonic summons have the tendency to go berserk, so the spell was usually use to obtain sacrifices for rituals and skills.
 * Create Undead: A 3rd tier spell that allows the user to spawn a low-tier undead minion.
 * Summon Angel:: A spell that could summon an angel, but ranged from different level of tiers. This is what summoned the Archangel Flames, Principality Observation, Principality Peace and so on. Moreover, there are a number of types of angels that can be called forth by using this spell. The only spells introduced by tier level is 3rd, 4th, and 7th.
 * Summon Household: It allows the user to summon a multitude of different familiars, such as vampire bats, rats, wolves, etc.
 * Summon Monster 10th: 10th tier magic; summon a high tier monster.
 * Summon Bicorn: It allows the user to summon a Bicorn to assist in battle.

Super-Tier Magic

 * Iä Shub-Niggurath: Summons a black cyclone and kills everything in the area. The victims are sacrificed to summon monsters over level 90, "Dark Young". The number of summoned Dark Youngs is proportional to the total number of sacrifices used for this super-tier spell.
 * Pantheon: Summons 6 level 80, "Cherubims Gate Keeper" through the use of Super-Tier, holy-type magic under his command.

Rituals

 * Death Spiral: It is a magic ceremony conducted by multiple magic casters in a group to turn a metropolis of living people to a spawning place of undead.

List of Summoning Items

 * Sealing Crystal
 * Horn of the Goblin General
 * Armageddon Evil
 * Staff of Ainz Ooal Gown
 * Statue of Animal - War Horse
 * Moon Jade

List of Summoners
Summoners are individuals who're capable of conjuring minions from different races. Some of these individuals also happen to be a Magic Caster. Through various means in being able to summon one, the user would ranged from one's racial levels, class levels, abilities, skills, tier spells, to items.

If summoners in the New World possessed a Talent related to summoning, it can give them the advantage of strengthening their summoned monsters by a slight margin, etc. Moreover, unless their summoners were specialists, summoned monsters were generally weaker than the ones who called them forth.

With multiple summoners in one group, it is possible for them to conjured monsters as a form of military army. After their previous summoned entities were killed in battle, they can still continue conjuring more of them one after another continuously as long as they have enough mana provided to do so. By doing this, the group of summoners can overwhelm their foes with numbers no matter how weak the summoned entities may be to the opposition.

In other words, even if the summoned entities vanish, the summoner can keep on summoning more of them from behind to fill the gap. While so, these newly-summoned entities will continue attacking in place of the absent summoned entities. Since summoned entities were beings that did not die even when they are killed during battle, they could somehow be fully utilized in this kind of fashion.
 * Ainz Ooal Gown
 * Shalltear Bloodfallen
 * Demiurge
 * Albedo
 * Sunlight Scripture Members
 * Nigun Grid Luin (capable of summoning an angel via using a consumable item)
 * Calca Bessarez
 * Black Scripture Members (capable of summoning an angel via performing a ritual together)
 * 5th Seat of the Black Scripture
 * Khajiit Dale Badantel
 * Iguva=41
 * Rigrit Bers Caurau
 * Entoma Vasilissa Zeta
 * Kyouhukou
 * Kelart Custodio
 * Crusch Lulu
 * Enri Emmot (capable of summoning goblins via using a consumable item)
 * Lizardmen druids of Great Lake

List of Summoned Monsters
While summoned monsters shared a certain degree of knowledge with their summoners, said information was quite random and disorganized. It would be best to regard it as the ability to tell friend from foe. Therefore, it was important to give verbal commands to summoned creatures.

Summoned monsters could be banished in several ways: when their summoning time ended, when they took too much damage, or when their masters manually dismissed them. When a monster is banished from taking too much damage, it was a common tactic to immediately re-summon another monster of the same type.

Undead

 * Death Emperor
 * Death Empress
 * Eternal Death
 * Eyeball Corpse
 * Grim Reaper Thanatos
 * Overlord Wiseman
 * Pale Rider

Angel

 * Seraph Empyrean
 * Seraph Aesphere
 * Cherubim Gatekeeper

Undead

 * Corpse Collector
 * Death Knight
 * Elder Lich
 * Jack the Ripper
 * Soul Eater

Angel

 * Dominion Authority
 * Principality Observation
 * Principality Peace

Undead

 * Bone Vulture
 * Skeleton
 * Wraith
 * Lesser Vampire
 * Vampire Wolf

Angel

 * Archangel Flame
 * Angel Guardian

Demon

 * Devourer
 * Gazer Devil
 * Hellhound

Spirits

 * Primal Air Elemental
 * Primal Earth Elemental
 * Primal Fire Elemental
 * Primal Star Elemental
 * Primal Water Elemental
 * Swamp Elemental

Undead

 * Death Cavalier
 * Undead Lieutenant
 * High Wraith

Goblin

 * Goblin Troop (or otherwise currently known as Goblin Army)

Unnamed Race

 * Dark Young
 * War Horse
 * Bicorn
 * Moonlight Wolf
 * Snap Grasp

Ninja Monster

 * Hanzo
 * Kashin Koji
 * Fuuma
 * Tobi Kato

Unnamed Race

 * Beast of Burden

Trivia

 * Let alone a Super-Tier Spell like Iä Shub-Niggurath, there exists a special ritual that also requires a living sacrifice or more to be carry out for summoning a monster.
 * Although a summoned undead such as the Death Knight can stay active permanently via a dead corpse, it doesn't work the same way with a Super-Tier Spell. The summoned monsters created from the usage of a super-tier spell stays in the world for a limited duration temporarily and are not permanent.
 * Summoned monsters like the Death Knight have abilities for example that are capable of causing weaker beings than themselves to appear through the target it killed.
 * Ainz and Enri are the only two individuals to keep their summoned monsters around permanently while other summoners in the New World can't keep theirs around for long. Unlike the summoned undead or goblins who were shown to have the potential to stay in this world permanently after being summon, other summoned monsters for now haven't been able to do the same. Although the summoned monsters' presence is temporary, Ainz's summoned undead in particular had that problem solved with the use of dead bodies or body parts while summoned goblins are permanent because of the item, "Horn of the Goblin General" used by Enri.