Samus is his worst MU. Impossible to kill. she never dies upright (upsmash and nair kill at like 150 on stadium) most of his good edgeguards rely on forcing people to use their resources early with peanuts/throwing bananas vertically to cover a slide just past the ledge, samus can out stall most of this while keeping her jump with bomb stalling. Neutral can be rough, we have tons of means to deal with missiles but getting in is hard and we don't get lot per hit (like 20-30% per winning exhange, and she dies at 150+ consistently in this MU), while we take 70~% or die to a charge shot for a mistake. Its rough. Junebug switches to ganon now after trying 2 sets vs plup at smash and splash. Other floaties can be hard because killing them is rough, but we control neutral vs all of them sept zelda, who we can just time out if it comes to that.
Fox is slight disadvantage because he can stop us from pulling bananas and running shine ****s us up, shine still kills us at zero by the ledge. nothing too bad, we can reaction tech chase him and chain grab him to death from zero (dthrow to 40ish, then upthrow chaingrabs) and we can actually kill him. I find wolf to be hard for similar reasons, we can kill wolf really easily though so its probably even enough to not worry about. Rising nair from ledge ****s wolf's recovery.
I'm convinced we lose to yoshi because we have no throw followups on him at any %. Camping him only does so much when we die from one combo and can't kill him without stray hit>cliping his double jump.
Sonic is a pain but thats just the character, its not too bad.
IMO, diddy's losing MUs or just hard MUs are (in rough order):
Samus (Only MU I think that is worse than 60/40)
M2 (similar reasons to samus, plus his item counter-play ceiling is the best in the game. M2 with a banana in hand is IMO the best character in PM)
Fox
Wolf
Yoshi
Snake
Peach
Hard MUs where its probably even or we win, just a pain:
Zelda
Luigi
Wario
Sonic
ness (**** guaranteed dthrow chaingrabs to 80%)
Zard
GnW (gotta lame him out)
Other than that we go even or beat everyone.
I think Diddy's most important winning MUs he has for him are:
Falco (throw bananas to punish laser rhythms, do the junebug edge guard to cover all options and he dies at any%. check the video analysis by june of aero vs Rscizzle)
Falcon (venom disagrees but I think diddy wins super hard)
Lucario
All of fire emblem (having a banana in hand dwarfs the range control that marth/roy have. whiff punish DD dtilts with a glide toss, at worst you get them to shield and shield advantage. Ike gets bodied in neutral because he has to comit to something eventually then you blow him up. Plus they are the perfect combo weight. one grab is like 50%, you only need to win 2 on stage interactions and get the edge guard to take a stock.)
ROB (I think diddy has the edge since the weight/fall speed changes to rob, but its mostly theory smash because we don't have any super good ROBs in AZ [ Or any actually good Diddys lmao]. something something diddy has to commit less, some thing something wins neutral, combos rob super hard, etc)