Never has there ever been such an odd mix of disgusting and creepy.
Known simply as ??? when Link writes about helping him in his Bomber's Notebook, this creepy guy lives in the toilet in Clock Town's Stock Pot Inn. No, not as in “he's constantly using the toilet and therefore spends all his days on the john”, no. He literally lives in the shadowy depths beneath the toilet seat.
During certain times of the night, Link can approach the bathroom to be greeted by his green, pasty, outstretched hand, followed by a plead for “Pa-pa-pa-paper!”. If Link complies with the questionable request and hands him any of several property deeds or letters he was asked to deliver, the unseen and unsanitary ghoul upchucks a Piece of Heart for his troubles.
When he made a cameo appearance in Oracle of Ages on Game Boy, Link gives him some stationery (presumably to wipe his nether-regions with like in Majora's Mask) as part of a trading sequence. He's rewarded with what's described as a “Stink Bag,” which someone else in the world bizarrely has a great need for.
In this game, he can be attacked by dropping various seeds down the loo, or even bombed. To make him even creepier, if Link manages to fall down his hole, he does not survive the drop. Was it the smell? Did ??? eat him? Nobody knows.