Some things not mentioned yet:
You can pick up bananas with dash attack, any aerial, or an airdodge.
Your bananas can and will be used against you. I prefer to have only one banana in play just to easier keep track.
Down B has two ways to pull. Smash down B and tilt down B. Obviously smash version tosses higher.
Peanut Popgun can be canceled in the initial frames with shield. I use this for aerial turnaround to toss bananas. Peanuts can also be caught by enemies and throws at you.
You can spike with Rocketbarrel’s blast.
You can cancel the Rocketbarrel’s usual descent by using your second jump at the same time as UpB. It will go upwards as you charge. this can only be done if you are hit first.
Nair might not have KO power or priority, but it is still an important move. It is AFAIK his quickest aerial (pretty sure quicker than Bair, even though it recovers slower) and since it has low knockback it is very useful for comboing.
Dtilt is nice. It has little knockback and can be chained into itself or Fsmash at medium %.
Since Diddy’s best KO moves (Fair, Fsmash) don’t have the greatest knockback to begin with, make sure you don’t spam them, since successive use of moves causes them to decay in both damage and knockback.
If you try to spike by coming from below then using Dair, you leave your self very open to spikes yourself, and also footstool jumps. Coming from above is IMO the best way to spike with Diddy.
Also, airdodge does not add any distance to recoveries. This was disproven already. Arguably his best recovery is SideB, DJ+UpB.