Rupoor

A Rupoor is a black Rupee-like item that appears in Phantom Hourglass. It is first encountered on the Ghost Ship, after one of the Cubus Sisters advises Link to gather treasure from one of two chests. Opening the chest that the Cubus Sister recommends results in Link finding a black Rupee, a Rupoor. Their only other appearances in the game are on Harrow Island, in which you can find 10, 50, and 100 Rupoor, and in a maze found in the northeastern quadrant where instead of walls the maze is made of 10 Rupoor and 30 Rupoor pieces. The result of collecting a Rupoor is that its amount will subtracted from your wallet. Whenever Link finds one, the traditional item music plays but fades away midway. Link also has a hurt expression on his face when they are found.

Twilight Princess
Although the Rupoor never officially appeared in Twilight Princess, an image of a black rupee can be found through hacking and often replaces items on the item screen if they are hacked out.