A few things I've found but haven't added to my guide:
-press a jump button while hanging on the edge of any level, and diddy will perform a ledge-jump as all characters do, right? Because of the minimal lag at the top of this jump, you can throw a smash banana behind you and use it to assist in edge-guards. If you knock your opponent off and do it immediately, it will come in handy as its on its way down. I've once faired an incoming opponent, grabbed the flying banana at the same time, then tossed it at them as they flew away. I edge-hogged them at like 20% for the kill.
-throwing bananas right at the edge is a really good thing to do. It kills alot of their options. If they ledge-hop you can intercept them easily. If they attack/roll, chances are they'll slip on the banana. Throwing one out there is a big advantage when pressuring them off the stage.
-run at your opponent, R.A.R. then throw a banana. Don't get too close, they'll punish you for it. Its only use is to provide something to work with when approaching.
-Try to always have a banana in your clutches, it really helps in the grand scheme of things. When recovering, you can knock opponents out of your way and diddy hump them, or safely recover afterwards.
-In the same way, when edge-guarding, you can jump straight out and hit your opponent with your banana mid-air, then fair or dair them after they take the hit. Its a deceptively useful edge-guarding tool as well.
Hope this helped.