Ruyi Jingu

Very rare weapon
(a.k.a. Yeoui) is a sacred weapon that is used by the Monkey King of the Nine Kings. The Staff, together with Kinto-Un and Gourd, forms Weapon of the Three Gods, The Monkey King's Weapons of Choice. The Ruyi Jingu takes the appearance of a silver bo staff.
(Effects) Magical bludgeoning damage
Quarter staff 1d6 damage
Can spend 1 ki point to extend the range of an attack by 15 ft as the staff itself extends Or spending 1 ki point the staff extends in a straight line to 15 extra ft and anything in that area makes a DeX save (16) or take 1d6 piercing damage and is pushed back to the staff's length