The biggest issues I saw were habits. It seemed like for certain situations you had 1 preferred response, and you'd occasionally get punished for it once the fox caught on. The ones I noticed the most were:
1. Whenever you're on the edge and Fox comes anywhere near you, you drop->doublejump->uair back onto the stage. This works great if it hits him, because most often it will send him back off the stage while letting you on. It has pretty terrible range in front of pikachu and the hitbox starts behind pikachu before travelling forward and causes your hurtbox to hang a little just above the stage while you do it. This means if he expects it, it's easy enough for him to just fake approaching the edge, stop short, and then punish your uair by either hitting it in landing lag or just beating it with a number of things (usmash being the most notable) once you're out of ledge-invuln. He does this a couple of times, and kills you at least once.
2. Somewhat related to 1, you tend to hang on/around the edge a bit seemingly in hopes that fox will rush towards you and you can catch him with something. This is fine to do occasionally, as immediately getting on the stage from the ledge is punishable too, but again all fox has to do to punish this is fake an approach and calmly punish whatever you try to trip him up with. And for clarification, playing near the ledge but on the stage is fine in general, as you're constantly threatening grab->bthrow and other shenanigans, but repeatedly returning to the ledge (drop->dj regrab, upB stalling, etc.) isn't a reliable tactic. If the opponent sees it, it's pretty clear what your intentions are. In general, wding onto the stage should be your most common return from the ledge, but of course, mix other stuff in (like this option, or upBing straight forward onto the stage, or upBing to a platform, getup attack, etc.) to keep em guessing.
3. When holding the edge and ledgeguarding a Fox, you would drop or jump back and try to aerial him I think every time. I'm guilty of getting in this habit too sometimes, because pikachu can do it pretty safely and it feels good. But there were a couple times where you could have just ledgehogged and it probably would have killed him. If it didn't in those situations, you would have had time to drop->dj uair to pop him back off the stage anyways, or wd on->grab->bthrow. Part of this is working on edgeguarding, so if you go for the aerial every time, make sure you can make them hit and preferably kill him. Fox has enough variability to his recovery that it can be difficult to properly edgeguard with a drop/jump aerial from the ledge. If he's far enough out/down though, his recovery can only get him either to the ledge or barely onto the stage. In this case with proper ledgegrab timing (to refresh your ledge invuln) you can ledgehog him if he goes to the ledge, and still leave the option of wding onto the stage to punish him if he reaches the stage (and you have good reactions).
4. You upB'd to the ledge a lotttt, and liked to hang out off the stage at a distance where doing so was comfortable (same up->diagonaldown trajectory almost every time, occasionally just diagonaldown). This generally made your recovery plans pretty clear, and you got ledgehogged a couple times because of it. Technically speaking it's a pretty safe way of recovering, but obviously punishable if Fox expects it. You can make this a little more ambiguous by getting used to different angles (which allows you to recover to the ledge from different distances, making your intentions less clear), but mostly just mix up where you recover to. Recovering to the stage is less safe, but occasionally just doing it (and not because Fox is already on the ledge) is enough to keep Fox guessing. It's worth it to recover to somewhere where you may get slightly punished (i.e. by like a nair or bair if you go to a platform) once or twice in order to make Fox hesitate a little bit when you're off the edge. Were I the Fox in those matches, whenever you were recovering the main things going through my mind after a couple times would have been "Am I able to safely ledgehog him from my current position?" and "Can I make this ledgehog not look too obvious?" What I SHOULD be asking myself is "Where is he going to recover to?" but you didn't give him much reason to. You seemed to mix up your recovery only out of necessity, when the ledge seemed unavailable. Mix it up, make him guess. Getting ledgehogged kills you, getting hit with an attack because you recovered to the stage a few times usually won't.
5. This isn't so much a habit as a decisional question, but a few times that you would get a rising uair on Fox near the ledge as he tried to recover and you chose to usmash him afterwards. I don't remember if it really led to anything any of the times, but it generally felt like grab->bthrow would have been a better option pretty much every time. It's less damage, but at that percent usmash isn't going to kill and bthrow at least puts him back off the stage and could result in a kill. Just struck me as an odd choice, and seemed a consistent one.
As a last note, and this was a lot less common and may just be my personal preference, but it seemed like Fox was trying to take advantage of your hesitation to hold your shield around him. I know Pika's shield sucks, and downdodge or uair out of shield are pretty good, but often he'd just throw out a usmash if he was next to you or dash past you and turn around to wait for you to jump, then hit you with an aerial or something. It felt like if Fox was on top of you you'd just kinda panic and shield, then jump out after about a second. I would have liked you to occasionally just hold your shield (probably lightshielding to an extent) longer and see what he does. If he commits to a punishing usmash or bair/nair, you shielded it and might be able to get something out of it. If he keeps running around you/waiting for you to jump then yeah you're going to have to drop your shield and do something eventually, but the timing isn't so telegraphed and you can still wd out or jc->usmash (or just drop it and slow walk forward for super pro mindgames!) out of it instead of jumping. If he grabs you while you're shielding, then it's not so bad because it's Fox (as compared to mario or sheik or etc.) His options from grab are uthrow->uair (which you can smashDI if you're comfortable with that) or fthrow/bthrow for no real followup and meh damage, or dthrow for a techchase option (which he's pretty much guessing on the punish). All of those options (assuming you smashDI/avoid the uthrow->uair) are much better than getting usmashed when he predicts your jump. As with anything, don't rely on shield, but it's fine to use it for a while occasionally to tell Fox that he can't just usmash whenever you two are next to eachother.
Otherwise it looked pretty good. You seemed to have a cohesive plan throughout the matches and, with a few tech errors which happen, went through with it. You seemed pretty comfortable handling pikachu and knew what works on Fox. Just try to be a little less predictable and i think you'll do even better.
Edit: Also, about what you found out about Bair dkuo:
That's pretty interesting! Melee has some random stuff in it, keeps surprising me. I doubt it has much strategic worth (maybe!), but it's still pretty cool to know.
