Y, possibly Yboxfan997, is a character used by SMG3 as a ripoff of X. He appears briefly as part of SMG3's copy of War of the Fat Italians, during SMG4's blooper Smg4 vs. Smg3.
Y has a color code that has also been used for Bot and Barbie's son. It is reveled in Italian Kidnapping that he and Bowser met in toilets.