World Tree YGGDRASIL

World Tree YGGDRASIL is a tree that has its own backstory and lore set for why players ventured through different worlds of YGGDRASIL.

Appearance
It is a tree that sprouted over countless leaves, ranging from more than two hundreds of it overall.

Background
The World Tree YGGDRASIL had its own vast wealth of leaves get eaten by the Devourer of the Nine Worlds, causing them to fall one after the other, until only nine were left. These nine leaves from the World Tree were the previous incarnations of the Nine Worlds: Asgard, Álfheim, Vanaheim, Niðavellir, Midgard, Jötunheim, Niflheim, Helheim and Múspellsheim. In the game, the World Eater continues to make advances toward the nine remaining leaves or worlds which players must try their hardest to protect from that particular World Enemy.

On the other hand, by comparison alone, each one of the World Items are created as the sole equivalent to every leaf that hailed from the World Tree other than the nine worlds. Particularly, most if not all of the two hundred World Items were found scattered randomly about in the nine worlds. They are very likely to share a deep lore connection with the World Tree. For instance, one of such world-breaking items from the game happens to go by uncanny names like YGGDRASIL Leaf, Seeds of the World Tree, and so on.

The Bloody Valkyrie Arc
Ainz recalled the brief history behind the nine worlds and the many World Items that had its origins trace back to the World Tree YGGDRASIL.

Abilities and Powers
When the World Eater had greatly consumed parts of the World Tree YGGDRASIL, it was mentioned how several leaves fell off from the latter's branches until the last nine are left untouched. The World Tree's former leaves were closely comparable to the power level of the World Items found existing in the game. As World Items are made from remnants of the fallen leaves, they are scattered about all over parts of the nine worlds for players to uncover during the course of their vast exploration.

While Ulbert Alain Odle was readily casting his [Grand Catastrophe] spell, it was said that the fallen leaves of the World Tree YGGDRASIL had a cursed malice of their own. If his spell ends up taking full effect upon its successful casting, the leaves' curse would be given a physical form of destructive energy that will surge through the battlefield. This may suggests the notion that other unknown Tier Spells out there apart from the one used by Ulbert may have some powers connecting back to parts of the World Tree too.

Trivia

 * Each leaf from the World Tree are said to be the symbolic representation of all the nine worlds and two hundred World Items whom are existential to the game.
 * In the New World, the floating city of Eryuentiu formerly owned by the Eight Greed Kings was said to have a meaning behind its name similar to the World Tree YGGDRASIL. According to Fluder Paradyne, it means ‘the tree in the center of the world’ in an ancient tongue.