http://www.youtube.com/watch?v=EJx-ZuKTnvQ
First video I saw of Kos-mos
I heard that Wolf can be diddy's hardest matchup thanks to Autocancelled Fair instantly picking up bananas and it gives him something to DACIT into Dsmash with.
Oh, and a floating peach=popgun. She's always right in the arch.
That was from January. People and matchups are able to change from then. Kos-Mos decided to severely change the way he played his Peach and the matchup and improved in it drastically. Kos-Mos has beaten ADHD, NinjaLink, Le Thien, and others, basically becoming THE Diddy slayer.
More recent matches:
http://www.youtube.com/watch?v=N4KesI4p3bU
And the thread where Le Thien talks about the Peach and Marth matchups
http://www.smashboards.com/showthread.php?t=195024
Why Luigi is listed as one of Diddy's hardest matchups, I'm not sure. Even though Luigi slides when getting hit by bananas, eliminating most of your followups, his range is horrible. Your fair outranges like everything he has, and you can camp much more effectively.
It really should just be Peach and Marth, but in his thread that I posted, we're already contemplating that Diddy vs. Marth could be even with mid-range game. So eh.
Wolf definitely isn't Diddy's hardest. It's difficult yes, but at mid-far ranges Wolf can't do much.
Diddy vs. Falco is even. The reflector isn't even a problem because throwing bananas straight to anyone is stupid anyway. If they spam it, you can monkey flip kick over it, and if they like to use it, then you can bait one by approaching, dribbling back, and monkey flip kicking. You can always do short-hop or full-hop downthrow approach and he can't do like anything about it (he can't do much when you're above him regardless). Falco doesn't really have much on Diddy, IMO it's slightly Diddy's advantage.
Diddy vs. Wario is slightly Wario's advantage, like 55-45. Wario's aircampiness makes your banana power diminished, but unlike Peach and Marth, he doesn't have great aerials for catching them, and unlike Peach, he can't instantly reclaim bananas once a throw has been whiffed. If he's on the ground, Bite is really good for him, although you can do a short hop dthrow and fast fall fair and punish the very slight lag he gets from eating something.
Wario doesn't have good range, which is something you have to abuse in the matchup. Yay fairs. Still, it's his advantage, but not as bad as Peach, IMO.
Anyway, onto the current people.
Wario-Marth
ROB-MK. Even though ZSS has an infinite on him, dsmashes don't often happen, especially not well spaced like it has to be. Rob can still just camp her out and avoid Dsmashes all together. I'm not sure how the matchup is without the infinite though.
Lucario-No clue, lol.