World Items (ワールドアイテム, Wārudoaitemu) or World Class Items (世界級アイテム, Sekaikyū Aitemu) are the most powerful and legendary items in YGGDRASIL. They possess massive power that could potentially threaten the game's balance, thus, earning them the term "Balance Breakers." They are also known to be called the "crapped out."
In the game lore of YGGDRASIL, the World Tree was once covered with a countless number of leaves, but one day a gigantic monster appeared and devoured these leaves. The leaves were destroyed one by one, until only nine were left, making the Nine Worlds of YGGDRASIL. These World Items are said to be made from remnants of those leaves, each equivalent to a world in power. The monster that devoured the original leaves would attack the remaining realms for these items. They were integral to the background story of the game: Players would step out into the unknown and face dangers in order to protect their own world.
In all of YGGDRASIL, there were only 200 World items. Each of them had their own unique ability, and some were powerful enough to destroy the game's balance. Of course, not all of the World Items had such game-breaking abilities. Even so, if a player managed to get hold of a World item, that player's reputation in YGGDRASIL would jump to the highest level. Effects of a World Item can be resisted in only two ways: (1) Owning another World Item. (2) Getting special Job Classes.
While this is just speculation, there was a guild that said even a World Item may possibly drop from level-breaking bosses. In particular, this being the Lords of the Seven Deadly Sins since they're classified under YGGDRASIL as a World Enemy. The guild believed that through defeating all seven of them, the World Item would appear from the monsters, finally dropping it.
Normally, World Items could not affect holders of other World Items and would be a different matter unless those holders happened to accept that influence. All of which was made possible thanks to a patch created by the developers of the game.
In the New World, it was revealed that many World Items had been scattered about all over the continent. Apart from players, some World Items are owned by its native inhabitants respectively while the rest have no owner to lay claim to. Hence, these ownerless World Items are known to be discovered in various places such as ruins, fallen civilizations, and so on.
Known World Items
Twenty is the name of 20 World Items that are unrivaled in terms of power. All of them could only be used once. If one needs to be used again, one should find the item all over again, regardless of the difficulty of the process. The guild of Ainz Ooal Gown currently possesses two such items.
- Ahura Mazda: It has a potent effect on anything with a negative karma value, and its area of effect could span an entire world.
- Five Elements Overcoming: It has the power to request the developers to change the magic systems of YGGDRASIL.
- Longinus: It has the power to completely remove any target from existence at the expense of the user's own existence. There was no way to restore the data of anyone deleted by the World Item, other than by using the resurrection powers of other World Items; neither cash items or resurrection spells would work. If someone were to use it on an NPC of Nazarick, it would even reduce the maximum creatable levels of NPCs — the special feature of a guild's homebase.
- Ouroboros: It has the power to alter YGGDRASIL's game mechanism, in more ways than Five Elements Overcoming. This item once prevented Ainz Ooal Gown guild members from entering a certain area.
- World Savior: A club-shaped item, which is very weak in its initiatory stage, but gets stronger with time. It can become so strong that it could even conquer Nazarick with all the members of Ainz Ooal Gown combined.
- Unnamed World Item: May have the power to remove status effects, such as mind control, from any target. Currently stored in the Treasury of Ainz Ooal Gown.
- Unnamed World Item: Unknown power. Currently stored in the Treasury of Ainz Ooal Gown.
Other World Items
- Atlas: Currently, the ability of it is unknown. It once belonged to Nine's Own Goal, the precursor organization to Ainz Ooal Gown, but a guild stole it.
- Avarice and Generosity: A pair of gauntlets, which looks like a devil's hand, while the other it looks like an angel's. This was given to Mare Bello Fiore from the treasury.
- Billion Blades: Currently, the ability of it is unknown. This is given to Demiurge or Cocytus from the treasury.
- Caloric Stone: Its exact power is currently unknown. This item can only be gained by using massive amounts of rare metal from seven hidden mines. There was one that belonged to Ainz Ooal Gown. Nubo proposed to make invincible golems by using this item.
- Depiction of Nature and Society: A big scroll, which is given to Aura Bella Fiora from the treasury. It has the power to isolate an object to a different dimension.
- Downfall of Castle and Country: The user can mind control any and all beings, even with absolute mental resistances. It is currently in possesion of the Black Scripture and was used to mind control Shalltear Bloodfallen. 
- Ginnungagap: A World item that is equipped by Albedo. It can seemingly be used to destroy large areas. Tabula Smaragdina gave it to Albedo without permission from the rest of the guild. Ainz only noticed just before the game was about to end so he let it slip by.
- Hygieia's Chalice: Currently, the ability of it is unknown. This is given to Demiurge or Cocytus from the treasury.
- Nameless Book of Spells: A book capable of inscribing many old spells and new spells of Tier Magic that hailed from both YGGDRASIL and the New World.
- Seeds of the World Tree: A racial-change item used to transform into a different race.
- Throne of Kings: A prize was given to Ainz Ooal Gown for completing the Great Tomb of Nazarick in one go.
- Two-Worlds Mandala: A World Item that was once a National treasure to a country but was later stolen by New Ainz Ooal Gown.
- Graeae: A World Item that was under the possession of World Searcher. (Web Novel only)
- Holy Grail: Healing?-type (Web Novel only)
- YGGDRASIL Leaf: Protection-type (Web Novel only)
- Gjallarhorn (Gyararuhorun): A higher level version the Super-Tier Magic <(Written: Summoning of an Avatar of God) Call Avatar>? (Web Novel only)
- Founder (Faundaa): (Web Novel only)
- A Dove Brings An Olive Branch: (Web Novel only)
Unnamed World Items
- World Item that summons devils: An item that summons an endless legion of very strong demons, making a lot of trouble for Yggdrasil. It is unknown if it is one of the "Twenty."
- Momonga's Red Orb: Ainz possessed a World Item that comprises of many different powers. It can be said that one of such powers was very effective against Dragons. The Web Novel counterpart of Ainz has stated that it gets stronger the longer it's on him. If Ainz activates this item, he will lose some levels.
- World Item from the 8th Floor: Currently, the name and its ability are unknown. This once belonged to Aureole Omega. Now the item belongs to Shalltear Bloodfallen.
- Ainz Ooal Gown has eleven world items in their possession. Compared to other guilds, there was quite a gap, since the guild after them only had 3.
- According to the game lore of YGGDRASIL, the World Items are made from the remains of fallen leaves from the World Tree.
- The World Items have the power to override「Wish Upon a Star」's magic.
- Most of the World Items abilities are superior versions of Super-Tier Magic.
- The Great Tomb of Nazarick's interior is protected by having World Items against World Items.
- During the formation of Ainz Ooal Gown, about fifty World Items were discovered.
- According to Maruyama, there are actually World Items other than the Twenty that are one time use such as the Caloric Stone.
- In the Web Novel, fearing the prospect of their respective World Item getting stolen, owners of such items will desperately conceal the fact that they have one. Information concerning the discovery of fifty World Items was gained by dishonorable means such as spies, information-type magic, leaks from Players who left guilds.