I would like to help but I am like the worst person to explain shiz to others about mu's =/
let's give it a try then =)
Ok first off some basic stuff you guys probably know.
Diddy is a quik character with a lot of fast moves that can string together in a lot of combo's
and since we are heavy and big it's even more dangerous for us.
Diddy's biggest threat though are his banana's.
Diddy's banana's are his evrything. He can do almost anything with it.
But we have a decent banana game as well =)
Dk can do some dangerous stuff with banana's and he does hace one of the longest glide tosses in the game as well.The thing is that both dk and diddy have an great ground game and decent air game.
The thing is that staying grounded is really unsafe at some points because diddy can controle the stage really nicely.Although Diddy's banana's are great they are not undefeatable.Things you should now is that diddy will throw a lot of banana's in your face. If you shield banana's don't let them just fall on the ground because diddy is there to pick them up again.In stead sh and z catch them. what most diddy's can do if you shield banana's is comming in and grabtry to dtilt that uproach.When a banana hits you be prepaired for the smash attack and DI it properly dk can live to 170 with this way.And form my own experience it's really driving him crazy.
Outside of banana's diddy is still good.
He has 3 amazing tilts,4 amazing arials and a good grab.
First off the tilts.
Diddy's tilts are actualy really dangerous at some points
His utilt can hit though platforms while you are on it so watch out for that.
It's also a good vertical koer which is where dk is killed earlier than verticaly.
Try to evoid this move in low percents because it ce nreally string in other moves like another utilt or an arial.
Dtilt is almost the same situation it can hit you multiple times and it has amazing follow-up's like sideB,Grab,usmash and fair watch out for a patren with those follow ups and try to read them
His ftilt is an amazing spacing tool but we have our own ftilt and our dtilt which can both outrange his ftilt.
This move is not used to often but it can kill and it will kill if you don't be prepaird.
Out of a banana trip this move can be used if the diddy is to far away for a smash so try to expect it and DI =)
Dddy's arials are really good especialy fair whitch is an amazing move and it's dangerous.
Fair can hit you out of your upb iirc. not sure about it correct me if I am wrong =)
Diddy's bair is good and fast it can string an tilts or another one so wach out for that.
His uair is faster than you should think it hits on frame 2 yes peeps frame 2 which is uberfast.Diddy can use this move for cambo's or maybe a bit of jugling.Do not spam Air dodge because diddy will eat it with banana's and Uair.
Diddy also has the dair which can do early kills. (watch out for dash attack to dair) Its a true combo's and it is dangerous for us.
His peanut gun is actualy really good if diddy has an banana in hand and in front of him.Do not uproach if he has this. just wait till the grounded banana is gone and uproach.
His jetpack recovery is easely gimpable with bair and it is actualy really anoying for diddy.
DO NOT GET UNDER THE BARRELS never. You will get spiked and you die.
Rather stay on the stage and let him come back if you do not trust it =)
And ofc his sideB I don't know how to explain this.
It's amazing sometimes diddy will throw this out at mid distance.And it can do 15% damage.
It's a great mixup for him but if you can find a patren in the uses from diddy. Punish it aspeciale the kick is punishable.
Let's go a bit farther on this move.
He has a few options with sideB
1.He can hump
2.He can kick
3.He can jump cancel it.
4.He can airdodge cancel it in the ground.
The first 2 are obvious.
But the third and fourth are actualy pretty good for diddy.
He can do a banana pluck out of the jump cancel and an tilt out of the groundcancel.
If he jumps out of it. you can punish it with uair which is great.
If he goes for a ground cancel just ftil or dtilt.If you are really brave go for an dsmash,punch or fsmash =)
A bit of a risk but a really high reward.
I think that sideB is an difficult move to handel but if you can see a patren it is defenately punishable by dsmash.
SMASHES
Ok so diddy has like evryone 3 smashes and they are actualy pretty good.
The fsmash is SDI able keep that in mind and punish it if you can SDI it. =)
The Dsmash is easely his best one and If diddy use it before 130% it's good for you.His best killer will get stale and you will only live longer
His usmash is a nice comboe'r and it is a really underrated move imo.
It can combo out of a dash attack and utilt even out of a dtilt it works.
BUT if you manage to shield it you can punish it hard. (Dsmash comes to mind)
Diddy's grab game is amazing.
With and grabrange as big as marth and snake it's really big imo.
He has a few good throws
What I myself like to do is fthrow or bthrow dash to my openent and regrab. they mostly just shield.
And I do get a regrab.the best thing after a diddy throw is walking/running toward or away from him.Do not shield they will read it and they will grab you.
The biggest advantage for us is that we live like twice as long as him but we can also get damage twice as fast as him.I find this mu a bit in his favour for 2 reasons
1.He can combo us and rack damge like it's nothing.
2.His groundgame and stage cotroll can be an isue
What you really want to do in this mu is getting at least 1 banana for your side so he can't string you that hard and you can use it if you know how.
Do not throw it off-stage. Diddy will just get a new one.
Just throw it somewhere so he cant use it.
1 banana on his side is better than 2.
The sacond thing you want to do is living as long as possible diddy can easely give you 100% but above it is more difficult for him to do stuff.He can't combo you as well and he can't really kill you good.(still need to mention that banana combo's will always work watch out for those)
The mu is 55-45 diddy's favour imo
because the ground is really unsafe for you and that's our best place to be in general.
As for stages Ban FD.
And go for Delfino,YI,Lylat or maybe BF if you feel confortable there.
Hope this will help people a bit and I hope I could actualy explain it a bit=)
Like I sed I suck at doing this but why not give it a try =)