Weird B is a glitch in Majora's Mask that manipulates the contents of your various B buttons. In MM3D, we can perform Weird B by using Epona, and Mask Storage.
To perform Weird B:
One useful effect of Weird B is putting the Great Fairy Sword on Deku B. This is done by performing Mask Storage with the Deku Mask. After dismounting, Deku Link will have the sword on B, but Human Link will have nuts. To fix Human B, simply redo the trick with Zora Mask, or Goron Mask.
Note that the above effects only occur if you currently have the bow.
By being Swordless, it is possible to write a bottle on Zora and Goron B.
To do this: