Actually, nvr mind. Honestly, you won't find one of Diddy winning because even MK's know better than to plank agaisnt good Diddy's. It just simply doesn't work.
I understand, we all have those crappy games where we just get pissed off about stuff like that but the key is, don't try at all. If he isn't trying than your best strategy is to do the same. Stay on the other side and shoot peanuts. When you see the opening, you go in with a banana. If he is camping on the ledge, pluck bananas close to the edge (not close enough for an attack.) Try and make them just barely graze the edge. If it doesn't work, who cares; you won't be the one stalling and being disqualified.
Puffster didn't know either and look at what happened to him:
http://www.youtube.com/watch?v=Fbmu8fGcWaw
EDIT: AvaricePanda left this comment on Youtube:
"A Diddy should never lose like this to a planking MK...a Diddy shouldn't even be trying to play gay in this MU anyway, or any MU, let alone vs. Plank.
It just guarantees loss."