Diddy's Up-b is deceptivly vunerable, It has bad hit-boxes and has a lot of landing lag, Where its really strong is how fast it goes, its flexibility, distance and how easy it is to grab ledge backwards. The Up-b has a long animation before you go into free-fall.
Diddy's arms and head are completely exposed which makes nairing and dairing him a breeze if you can intercept his arc. It also has 18 frames of landing lag so it is very punishable on landing, it just slides very far which gives the illusion of having a short landing lag. (previous builds [2.5] had around 8 frames of landing lag, in comparison)
I've been a lot busier than i thought I was so I'll just chime in in chunks. I also Lost my notebook which had all my MU notes (from diddy's perspective) which is really frustrating and put the video i was going to throw togeather back a lot.
Besides banana awareness and item control, a really important thing to note is that Diddy has pretty sub-par hitboxes. He maeks up for it through speed and bananas, but if you look at his aerials you'll see nothing extends past his hands/feet. His only real disjoints are rapid jab and <100% ledge get-up attack. F-tilt has a decent disjoint.
As you can see Nair has zero disjoints, so Ness's decent hitboxes should beat it out very well. If you see a Nair coming, retreating Fair will wreck it, as will well spaced nairs and Up-smashes. It is used in neutral more than his other aerials, and it is one of his two main combo starters. Nair has 9 frames of landing lag compared to Dairs 12, so Nair is the preferred launcher for combo starters out of neutral. Watch out for Nair planes as an approach, both the strong hit (the first half of the animation), and the weak one (2nd half) are great combo starters.
The rest of his aerials, Note how hitboxes are ehh:
Dair is his other launcher and is normally used in either tech chases, similar to how a Falcon will shuffle a Dair to cover certain options, like Tech in place or neutral get-up. Its also used as a combo ender and extender, Normally after a Nair, up-throw, Tilt, or side-b slap in order to force a grounded state on floaties. Diddy wants to keep Floaters like Ness close to the ground so he can play the tech chace/banana game and press his advantage the most he can, so look out for it.
It is the move with the best body-coverage he has so if you challenge it you'll normally trade, which in most situations is beneficial to Diddy. It is a meteor so be ready.
Heres the Diddy hit-box thread, its really good.
http://smashboards.com/threads/storytime-with-cranky-a-diddy-primer-for-3-0.331761/ Take a look so you know what you're up against and when his active frames are, what end lags you can punish, etc.
The Other main point I want to make, And is in
my opinion the most important thing after item control when fighting Diddy, is to
keep the pressure on. You don't neccesarrily have to always be doing magnet shield pressure or anything like that, but try to limit situations where he can pull out a banana as much as possible. If diddy does go for a pull, be sure you can punish it well, maybe with a grounded-pk fire, or if he jumped and did it, rising fairs. Alternatively just take it from him if he tosses it out towards you. Why this is important is that When Diddy resets the game to neutral, it isn't a "true neutral." I
f he get away and resets the situation, he gain advantage because Diddy's strengths lie in the neutral game. Its similar to playing a good lock-down falco, except that Diddy's neutral control is Dash-dancing with an Item instead of spamming lasers. Keep the pressure on Diddy, because by getting away he gains his advantages back.
since I lost my notebook, everything is a bit scatted haha. Idk, what is particular are people having problems with for Diddy? Diddy is a really flexible character so its not like you can employ one strategy and shut him down. Its all micro-situations and stage control and pressure, with both characters having a multitude of options in all the categories.