You-Know-What

The You-Know-What is a compact disc containing unknown content in Super Paper Mario to be returned to Bestovius in the Piccolo sidequest. Nothing else is known about it except it is a collector's item, as revealed by Bestovius after returning it to him.

At one point, Bestovius gives the item to Old Man Watchitt, but he never returns it, despite having been asked several times. When Mario arrives at his house to collect the Training Machine for Merluvlee, Bestovius asks him to get it back in exchange; because Bestovius refuses to reveal any details about it to Mario, however he simply tells him to ask Watchitt to give him the "You-Know-What," hence the name given to it as an item. The You-Know-What can be obtained only from Watchitt after obtaining Merlumia's autograph for him. Once Bestovius is given the item, he gives Mario the Training Machine.

Trivia

 * The Box is comparable to the Tape from Paper Mario and the Box from Paper Mario: The Thousand-Year Door. All are side-quest items that Mario is not allowed to see the contents of.