Dragon Quest II
The player can obtain an Yggdrasil Leaf by traveling south of the Sea Cave to an island with one tree on it. By searching this tree, the player can obtain the Leaf. The party can only get one leaf at a time from this tree and if the player already has an Yggdrasil Leaf, they cannot get another one.
Dragon Quest III
In Dragon Quest III, the player can obtain a leaf by searching the center point between 4 lone mountains northwest of Zipangu. Simlar to Dragon Quest II, only one leaf can be carried at a time by the player's party. Once used, the player can return to collect another.
Dragon Quest IV
Yggdrasil is a location in Dragon Quest IV. It appears simply as an immense tree hundreds of times the size of any real-world tree, with the elven village of El Forado at the base. Located slightly east of Mintos and surrounded by a ring of impenetrable mountains, it is only accessible by balloon flight.
The party visits it late in the game, after acquiring the balloon. After ascending to its boughs, they encounter Orifiela, a Zenithian who fell from the sky and landed in the Tree's branches. She helps them find the Zenithia Sword, which is nearby, and, after being rescued, agrees to show them the way to Zenithia.
Dragon Quest VII
In Dragon Quest VII, the tree, known as the World Tree in the game, can be found in Gröndal. When the party travels there in the past, the World Tree hasn't blossomed yet. It is a Sacred Tree. The residents of Gröndal, under the influence of a Fighting batboon, try to cut down the tree before it becomes a World Tree. The party stops this from happening and the tree is able to become a World Tree. The party can obtain a Yggdrasil Leaf by going to the World Tree. If the party does not have a Yggdrasil Leaf, a bird will drop one from the tree for the party to pick up and obtain. If they do, the bird will not drop one. They can also obtain a Yggdrasil Dew from Gröndal. However, only the Hero can get in line to buy one, and, if supplies run out before the Hero gets one, the party will have to leave town and enter again to try and get another one. If they already have one, they will not be allowed to buy another.
The Yggdrasil is considered the gateway to the realm of the Almighty, as when it blossoms the Starflight Express comes to ferry Celestrians. However, as part of the events of the game, when the tree blossoms, it instead causes a disaster in the Observatory.
The hero must venture down to the Protectorate to collect scattered Fyggs, which had fallen from the observatory in the disaster. It is later revealed that Yggdrasil is in fact the goddess Celestria, the daughter of the Almighty, Zenus. She became Yggdrasil to show Zenus that even though mortals were flawed, some still have good in their hearts.
The World Tree's Woe and the Blight Below
In Dragon Quest Heroes: The World Tree's Woe and the Blight Below, the World Tree is located in the kingdom of Arba.
Joker 2: Professional
In Dragon Quest Monsters: Joker 2 Professional, the Yggdrasil is a monster made by synthesizing Watabou (alias Fluffy) and Warubou.
Yggdrasil comes from Norse mythology. It literally means World Tree and it is the metaphorical "back bone" that supports the nine realms of the universe upon its branches.