Equip any mask of your choice (I recommend the Mask of Truth, Skull Mask, and Keaton
Mask), and go to the Lost Woods. In one room, there are two rock-shooting guys and
a bunch of bushes. In the bushes, there are some butterflies. Walk slowly around them
and you will fall into a hidden hole. Inside, you can have your mask ranked! It is
possible to get a Deku nut capacity upgrade (with the Mask of Truth) and Deku stick
capacity upgrade (with the Skull Mask) in here among other interesting reactions.