You-Know-What

The You-Know-What is a disc containing unknown information in Super Paper Mario that should be delivered to Bestovius in the Piccolo sidequest. At one point, Bestovius gives it to Watchitt, but he never returns it, despite him asking for it back time and time again. When Mario arrives at his house to collect the Training Machine for Merluvlee, he asks him to get it back; however, because Bestovius refuses to reveal any details about it to Mario, he simply tells him to ask Watchitt to give him the "You-Know-What," hence the name given to it as an item. He can only recover the You-Know-What once Watchitt gets an autograph from Merlumia. In return, he'll give Mario the Training Machine. He claims that he used to use it, but upgraded to a better, more compact design.

Only after giving it back to Bestovius does he reveal a single detail about the You-Know-What: it is a collector's item.