Against Diddy, it's pretty even cut, probably Diddy's favor, but it's a MU that I think Diddy's are far more developed in than the other way around. Lucario's edgeguard game+camp game with one banana is super useful against Diddy (Diddy always eats AS if he GT's if you time it right). Diddy fair is a pain in that MU though :\
On the subject of glidetossing, I suggest replacing FGT w/ JCGT (can also JCGT downward for forward dribbling). Not that it's recommended that you GT at a Diddy lol.
He can also dribble with bananas, which is nice.
The only true negative to Lucario is the fact that his Up-b is the only one in the game that has no hitbox. That leads him to get edgeguarded pretty hard which is why he has trouble with characters like D3 and DK who can just hit him off and throw hitboxes out there. I don't know much about this character...so I can't really input more than that.
rofl Lucario has the same thing to DK right back, fair n' dair absolutely wreck DK. Unless you were talking about MK, then yeah it's pretty sucky.
I agree that dair is pretty overrated, although it does help make his vertical zoning/fullhop game significantly better. One of the fewer characters that can afford to do fullhop aerials w/ only two jumps, although this often makes him prone to shield grabbing upon landing
roll is amazing, junebug's lucario lives for this move lol.
ftilt is pretty much fsmash's little brother. At this point most good lucs have learned to only use fsmash in places where the opponent is least likely to shield (aka landing frame traps, reading dodges/rolls, or if they're on the ledge). Pretty doable to PS on reaction, and unfortunately doesn't decrease release time significantly, so delaying it via charging isn't exactly as useful as it is for other chars (although it has a nice strutter-step).
I think something that's been very undernoted that might become more of a driving force in Luc's ground game is his noticeably fast dash animation. dash -> shield is very quick, which allows for faster true pivots, etc. Couple that with fairly large range attacks, and I think Lucario can have a fighting chance in ground control. He's very strong at punishing landings with a lot of frame trap potential.
His throws are veeeeeeeeeery rewarding. dthrow/bthrow for spacing/early game damage, uthrow/dthrow for juggling traps, uthrow for a few CGs, and fthrow for "equalizing" at high percents (pummels + fthrow in the 90%+ is pretty nice damage lol)
Luc upB is balls lol, although if there's gonna be a character that's forced to eat damage for it, it's gonna be lucario. Luckily, I think he has a much better time than say, Sheik, tether chars, etc. Has a decent cooldown landing onstage, curving def helps, and having a stall move, projectiles, and long DJ really helps (still is very edgeguard prone, but still).
Aura is fantastic, great mechanic for getting compensation for conditioning/picking up on patterns, also gives him some good tools against characters who lack in killpower.
BAS (uncharged Aura sphere) is pretty meh, not nearly as useful as it was 2 years ago.
uair, dtilt, and jab are really nice moves I love/think are underused. Usmash, DT, dsmash are kinda lacking in qualities of particular use.
Having good tools against jugglings a decent positive, B-reversals, nair, and dair stall are pretty handy for covering up landing.
And yes, he has transcendent priority, minus specials. Unlike MK though, lucario's limbs often extend a lot and allow moves to clank w/ them. Allows for decent fanning and such, but sometimes is a pain to deal with at times. fsmash, AS > 10%, usmash, and most aerials (although all of them suck at stopping it) beat tornado, just if anyone's wondering.
Aura is really handy w/ prediction/reads, which also makes him a worthy option for anyone who can pick up on an opponent on a player-by-player basis, which I think is his primary drive for doing better than he does on paper.
He's a smidgen fragile stage-wise, loves Frigate against most minus characters w/ better recovery. Loves neutrals in general, often stages good/bad for lucario are defined by blastzone size.
Might drop due to a slight cut in results with the absence of Zucco, but probably going to hang in high B/low A. Definitely a much better char in doubles lol.
Lots of solid tools, but an only "decent" character (especially in startup speed, bleh).
edit: Good **** Lee Martin