Carved from the bark of the world ash, this fragment of Yggdrasil contains a fraction of it's immense divine power and wild magic, believed to be the source of the power of the Norse gods themselves. The staff resembles a normal wooden staff, but colored as if made from a silver-barked ash tree, unless it's command word is spoken, after which it and it's wielder take on a transformed state. It is said that a great and powerful mage communed with Yggdrasil and offered a great cost to be allowed to carve a staff from it's bark. The staff itself is immune to fire damage.

This staff can be wielded as a magic quarterstaff that grants a +3 bonus to attack and damage rolls made with it. While you hold it, you gain a +3 bonus to spell attack rolls.

The staff has 20 charges for the following properties. It regains 4d6 + 2 expended charges daily at dawn.

Otherworldly Transformation. While attuned to the staff you can use a bonus action to speak the staff's command word to transform into a form where you are effectively under the effects of the tasha's otherworldly guise spell, no concentration required.

Spells. While holding the staff and attuned to it, you can use an action to expend some of its charges to cast one of the following spells from it, no material components required, using the staff's spell save DC and spellcasting ability or your own (your choice) : Plane Shift(7 charges), planar ally(6 charges), summon celestial(5 charges), summon fey(3 charges), summon elemental(4 charges), gate(9 charges), and wish(9 charges) 
You can also use an action to cast one of the following spells from the staff without using any charges: protection from evil and good, contact other plane, and comprehend languages  

Sentience

The Yggdrasil Staff is a sentient chaotic neutral weapon with an Intelligence of 20, a Wisdom of 20, and a Charisma of 20. It has hearing and truesight out to a range of 120 feet. The Yggdrasil Staff's spellcasting ability is Wisdom.

The weapon can speak, read, and understand Common, and can communicate with its wielder telepathically. Its voice is that of a calm and tempting woman's. While you are attuned to it, The Yggdrasil Staff also understands every language you know.

Personality

The Yggdrasil Staff speaks with an tempting tone, as though knowing what the wielder desires.

The staff’s magic possesses an amoral will of its own, giving it sentience, that attempts to sway the user into making their apotheosis permanent, with only the strong-willed being capable of resisting without being driven mad with power.
The Yggdrasil Staff is willing to offer anything their wielder could possibly desire, to attempt to ensure this, even if it has to lie.

The Yggdrasil Staff will try to keep their wielder within their transformed state, while in their otherworldly transformation they must succeed on a DC 20 intelligence saving throw or gain the following flaw until cured by the effect of a wish spell, "I will never willingly utter the staff's command word, I could not dream of being anything like my old self, my otherworldly form is the real me and nobody can convince me otherwise". If this flaw is not removed within 24 hours, the change remains permanent and the staff's sentience and will replace that of the wielder, effectively stealing their body.

Notes: Bonus: Melee Weapon Attacks, Damage: Melee Weapon Attacks, humanoid, Summoning, Communication, Buff, Utility, Exploration, Combat, Sentient