Rupoor

Rupoors, also known as Black Rupees, are black Rupee-like objects that appear in several games in the Zelda series.

Four Swords
Rupoors first appear in and are simply called Black Rupees. They are usually found hidden under rocks or grass, and if one of the Links picks one up, a random amount of Rupees fly out of their wallet. This can actually be beneficial: if the Links are under the influence of Rupee Fever (all Links have full health), the amount dropped can be doubled if they are taken back.

Phantom Hourglass
A Rupoor is first encountered in 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 10 Rupoors. Their only other appearances in the game are on Harrow Island, in which Link can find 10 and 50 Rupoor, and in a maze found in the Isle of the Dead where instead of walls the maze is made of 10 Rupoor and 50 Rupoor pieces. The result of collecting a Rupoor is that the amount that the Rupoor is worth will subtracted from Link's 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.

Skyward Sword
In SS undefined, Link can pick Rupoors up while he's digging during the Thrill Digger minigame and lose 10 Rupees. Using his slingshot on black Rupee Ore will also yield Rupoors.

On Fun Fun Island, Link can land on a "loser space," indicated by a Rupoor. If Link does, he must give Dodoh his Rupees.

A Rupoor can also be found in certain underground tunnels, for example in the tunnel nearby to the entrance to Eldin. Link can change Rupoors into Rupees of random value by sprinkling Glittering Spores on them.

Etymology
"Rupoor" is a portmanteau of "Rupee" and "poor."