My only explanation to that video is that those opponents aren't good players because an expert Fox player will completely kill a Mewtwo player without breaking a sweat.http://video.google.com/videoplay?docid=-5603712499325214933&hl=en#
It all depends on how you use him.
Jigglypuff is manly, not mediocre. You didn't play the game like a man resulting in you getting beatened by the manliest character of all time.And Jigglypuff's battling style could be considered "mediocre" as well, but all the floating she can do, added with her amazing midair attacks makes her an amazing character to use. I've fought a guy who beat the crap outta me with Jigglypuff. T^T