The Friend's Yo-Yo is an equippable item found in Mother 3. It can be used by Lucas, Duster, or Kumatora, and is presumed by many fans to have belonged to Ness. It is found in Thunder Tower, guarded by Li'l Miss Marshmallow. It provides +30 Offense and +5 Speed, and if shown to the Masked Man, Porky, Fassad, Mr Genetor, or any of the Pigmasks during battle, they will applaud. While comedic, this does not actually do anything other than provide a funny line of dialogue.
According to popular belief, this is a piece of evidence that contributes to the theory that Porky always thought of Ness as a friend and that he misses Ness very much. Enough to go into the past and steal it from him which could fulfill the promise he made at the end of Earthbound that the two will meet again. Further contribution to this belief is that Li'l Miss Marshmallow will refer to it as "Master King-P's very precious Friend's Yo-Yo".