The Cup is one of three objects of the 
Saber Expert puzzle, along with the 
Torch and the 
Ancient Relic. When filled with water, it unlocks the 
Rich Man's quest.
How to get it
In a house with a red door in the 
Desert: burn the brown curtain inside with the Torch to reveal a secret room that contains the Cup.
Usage
Equip the Cup and stand under the dripping stalactite in the 
Ability Teacher's cave to fill it with water. Then give the filled Cup to the 
Sick Man to unlock the Rich Man's quest.
Brigade
Cactus Petal
Candy
Candy Concoction
Candy Corn
Candy Egg
Celestial Token
Change Race
Common Scroll
Confetti
Conjured Cocoa
Core Brain
Cup
Cursed Scroll
Dark Fragment
Demonic Wisp
Dinghy
Dinosaur Bones
Disguise Elixir
Dragon Egg
Dragon Koi
Dragon Scale
Dragon Token
Easter Chalice
Easter Gifts