Rolling over Bananas won't help when Diddy doesn't have to commit to his defense, while you are already commiting to an offensive. This isn't even when he has a banana in his hand gnughuieaighzgyreh.
And I say grab-oriented because a good Diddy should be able to keep up a wall. Not impenetrable, but certainly a hassle to get around. Dash Attack would/should be punished with a Banana toss OoS, a Spindash Jump would more likely than not get punished with an aerial OoS, and blah blah blah. Mix-ups, mah boi.
Probably a good thing to do would be to get him in the air. Camp his landing, and make it so that he is afraid to pull bananas. The thing about a Spindash approach is that you become limited in movement, and not always can it jump at the right angle for attack, in which case Diddy will go unpunished for something that should've made him regret whatever it was he did.