I'm a bit lazy and I don't want to re-write everything I've said in the past, so I'll just quote it here. Some stuff might not apply to you, but the general idea does.
Training against one CPU is already a bad idea, so playing against multiple ones is really the worst thing you could do. Some things that work against a CPU don't work against a real player and some things that work against a real player don't work against a CPU. This will only result in you developping an anti-CPU playstyle completely inefficient against a human being. Simple examples: 1) Kirby's rock works everytime against a CPU and almost never (or really situationally) against a real player. 2) Spamming rolls to dodge attacks/move on the stage. And there are a lot more. If you played against real players (and good ones) often, then it wouldn't do much harm to play CPUs, but CPUs only is a bad idea.
Shielding is just one element of the overall passive playstyle one would develop against a CPU (again, because it works), and why would you do differently if you only play CPUs? You see that a combo is working against a CPU and you see that a passive* playstyle is working against a CPU, how on earth would you know (if you never play good human players) that the former is something beneficial to keep, while the latter is detrimental to your game? The dilemna holds true for anything that works against a CPU, thus so many Kirby's rock spammers and roll spammers among non competitive players.
*Just so we agree on the definitions, passive doesn't mean defensive. While it is arguable that a defensive playstyle is optimal (or at least very good) in that game, it's not the case of being passive. Being defensive means you work a lot on your spacing (ie putting space between you and your opponent, moving to stay out of their range), while passive is waiting and shielding an aerial then punish on the landing lag (for example).
Now with that in mind, and in addition to what was said above, I think that at your level, we can already see som stuff you do wrong. The problem is (cf my above post) that your things are working against a CPU, so you'll probably won't understand why we say it's bad. So either you trust us, stop doing these things and do worse against a CPU, or you don't and you'll have to play a good human player to notice.
-Learn to shield drop.
-Learn to z-cancel.
-Stop rolling.
-Don't use Up B offensively with Kirby.
-Use more Up tilts with Kirby.
-Don't grab so much with Kirby.
-Use nair instead of fair with Jigglypuff.
-You always edgeguard the same way, so you'll probably miss your edgeguards 99% of the time against a real player, but nothing you can do since CPU don't mix up their recovery.
-Learn to combo instead of spamming smashes.
-When recovering with Jigglypuff, using fair after an air jump makes him goes farther.
Your playstyle is the archetype of the CPU only player. You're doing well against them and because of that you might think
you're doing things right. In fact I believe you need to change your playstyle almost completely. If you really can't manage to set up online play (it's really not difficult though, and plenty of us are willing to help), then I'd say your best bet (assuming you don't have access to good human players) is to watch videos of good players and try to copy what they do. That's what I did with Falcon before I started playing online and got the basic U-air combos down. It will only get you so far though and you'll probably still be destroyed by a good player.
Do you still want the thread to be locked? Since I somewhat tried to answer your question, I'm waiting for a confirmation before I lock it.
