Yggdra

Yggdra, aka the World Tree, is a sentient tree with powerful magical properties. Her roots travel under the entire continent that contains Kauvet and connect the many planes of the multiverse. The world tree sits in Kauet's eastern swamplands near a hidden portal to the Feywild. There is also a physicalized mirror presence of the Yggdra in they Feywild itself.
During the events of Wake the Dead the arch-lich Vecna became imprisoned within the world tree. The proximity of this prison to a portal leading to the fae realm angers some denizens of the Feywild, an anger that Countess Olympia Mallinger and Quid the Reveler attempted to exploit to goad the Feywild into invading the material plane during the events of The Foe of Many Faces Returns.
Yggdra's hold on Vecna remains, but it has weakened over time, allowing Vecna to influence the mortals of the realm once more. He seeks out champions on whom he can bestow power in exchange for their fighting to free him. In order to combat this, Yggdra has begun granting boons to mortals as well, in the hopes that her champions will weaken Vecna's. He has succeeded as of Baba's Black Cauldron, as Arianwyn Phobos has become a champion of Vecna.