Preface:
For starters, do NOT be afraid of the grab.
Diddy is a character based entirely around controlling his opponent's ground options. He thrives on trapping characters on the ground and punishing landings. He has hands-down, the BEST OoS options in the game, and the fact that he can get a punish off almost any shielded move is retardedly good.
Unfortunately, Ice Climbers game revolves around grabbing, which beats shield.
As with every Ice Climbers match up, let's talk about separation. As in, how easy is it for Diddy to separate the Climbers, and once they ARE separated, can he easily kill Nana?
I think he can. Pretty easily, actually. -.- His d-tilt and u-tilt can send them in different directions and both come out EXTREMELY fast, his dash attack is excellent as a SPARINGLY used mix up, or when their shields are low, and his grab -> instant b-throw is seriously like 25 frames total. Crazy fast.
However, I don't think he can kill Nana as easily as most Diddy's believe. The most common way that Diddys use is spiking her, but as ESAM said, her erratic jump patterns can make her a little difficult to predict. Besides that, most of the time she is set up for a spike, it's because Diddy landed a grab. If the IC player is intelligent with ice blocks and jab, it can be pretty hard for Diddy to get in to get the grab.
I see so many players (not only Diddy) hitting Nana the incorrect way when she's running along stage, too. Her DI when separated from Popo farther than about three body lengths away is ALWAYS towards Popo.
So if, say, the scenario is like this.
N.......D...................P
On FD.
Don't hit Nana left. Start charging a f-smash RIGHT, and let her run through you. Her DI is in a right direction at this point, so hitting her left will give her good DI.
Don't try to play your mid ranged spacing banana bs against a good Ice Climbers (AKA not me).
Any IC player that uses Ice Blocks effectively to control the ground will **** you at mid range. Your much better off using safe approaches. Don't be afraid to get in there. You have safe options.
This sentence is an awkward segue into the next section: Bananas.
Bananas are what make or break this match up. If an ICs player knows how to keep your bananas from you and effectively use them to pressure you in shield and net grabs with them, you're probably going to lose, and it is the reason I think this match up is +1 ICs.
We have SO MUCH STUFF WE CAN DO THAT IT'S ********.
We also have two "characters" so we can get both nanas and camp under a platform REALLY HARD.
A good Ice Block while desynced can stop a banana mid flight and net a grab -> Nana shorthop instathrow down (Popo d-throws) -> Buffered Dash grab at lower percents.
Retreated bair beats your fair, by the way. Hue
huehuehue
I don't find blizzard to be an awesome move in this match up. When I'm Sopo I like it, but not really anywhere else.
Speaking of Sopo, he still has a few options against Diddy Kong on his own.
CG from 0-60 ish with a guaranteed f-smash at the edge, or buffered hyphen smash on stage.
Bair is still effective as Sopo, and we have plenty of shenanigans we can pull with blizzard mixups and other stuffs.
You don't gain a huge advantage from having just Sopo, unlike most other characters. The only significant advantage is that we can't 0-death you anymore.
On the edge, you have a pretty difficult time edgeguarding us if we're careful and mix it up. But getting on stage is a pain. I feel like d-tilt beats all of our options and is SUPER good pressure. You guys don't use that move enough. It's incredible.
From our perspective, we actually kinda CAN edge guard you. Bungee jumping and desynced Nana ledge grabs can ruin your whole charge up-b thing you usually do. If it's just Sopo, he can fall off d-air you for a kill. LOL. Ice blocks can gimp you if you aren't careful, and our d-tilt, if it hits around 80 and your dj is gone, can put you in a TERRIBLE position. It isn't easy to ledge guard you though, that's for sure.
I'm really tired, so this whole thing probably didn't make much sense or was all common sense stuff, but it's my perspective. P-1 seems to value my opinion but he's a troll so take it with a grain of salt.
Overall, +1 Ice Climbers if they know their banana game. Even otherwise.