Keeping a banana in hand and using popgun or just moving and controlling space is particularly powerful option. Popgun does crazy damage and KB now, compared to Brawl and every Diddy main in that game knows that keeping a 'nana in hand means that you're opening up your options at just about any time.
Especially for people who aren't familiar with the character (or people used to poorly fighting DDK in Brawl), you'd be surprised how effective [wait w/ banana in hand, shield/popgun] is (it also beats those people who want to grab your peanut on reaction). I won't go far as to say that that schema invalidates Luigi as a character like it does in Brawl... but, Luigi really has to work once Diddy has a banana in hand and is shooting popgun at him. Get used to Glide-tossing OOS and in every direction too, because they are all useful for different things. Pay attention to your opponents tech rolls and tech options, because he should absolutely terrorize characters with bad tech options like Falcon, GnW, ROB, Squirtle and the like in the tech chase game.
Get used to monkey flip, gentlemen. Seriously.
... Seriously. **** is borderline broken.