Just for the record, Lucario will probably either try to recover high to avoid gimping and expend his great offstage options like dair stall and floaty second jump, or a little trick they'll try to do is aim extreme speed straight up if they suspect a cape because that tends to still give them a chance to float (albeit in that crappy freefall mode) by not having to worry about getting caped the other way.
Lucario can and can't outcamp mario. Fireballs get outprioritized by Fully charged AS at about the high 30% iirc, so at that point be ready to do less fireballing because commiting frames to that could hurt you and be ready to zone to leave cape room to counter AS.
Someone mentioned range, which is definitely one of Lucario's features, but there's more to it that makes it different from someone like Marth for instance. Lucario is kind of the furry fiery version of MK, because he gets what's called "transcendent priority", meaning priority that cannot be canceled by another attack. The biggest problem is, that while the aura "bursts" are transcendent, his arms/legs aren't. That being said, this is why you get those weird lolsmash moments at high percents. Another thing that compliments his "safe" game is low endlag and aura's effects on his attacks. As everyone knows, aura increases damage, priority (on the limbs since other attacks need to become stronger to cancel his), and knockback (no, he doesn't get a boost in range, except the hitbox on his AS does increase). What most don't know is that aura also increases shieldstun from Lucario's attacks, making them safer on block the higher in damage he gets.
People are saying that they should be careful about Lucario at about 150%+. The truth is, he gets viable kill power as early as the 70% range. I would say you will definitely want to start getting Lucario to die from actually the 100% range, if you are aggressive you can tack on a lot of damage from punishes pulled off, and you have a solid killset that's decent at punishing bad moves too. The thing that's going for you is definitely that most Lucarios don't know this MU, but even at high levels of play Lucario has to be very careful with his attack pool.
If he dairs, a good one'll usually do it after the uair from dthrow, mario being on the ground means that Lucario only resets his situation. Basically it's a giant guessing game that neither player really benenfits from.
Lucario's gonna wall you, make sure you kill him by baiting fsmash or dair and retaliating with bair or your own fsmash (from the lean back it can punish fsmash most of the time) Lucario's endlag is what really sets him apart from many cast members, although startup is a bit on the slow side. Make sure you capitalize on every misspacing, Lucarios generally get a little lazy with this, and Mario needs every opportunity to tack onto him onstage.
Lucario's really good at keeping safe against lower tiers, so naturally he's going to use fair and it's mixups for taking the offensive if he has to (I don't think he'll have to at most points of the game) or bair/fair and nair walling defensively.
Lucario's zoning is really good fullhopped, make sure you're patient in punishing one that decides to go aggro. A good Lucario will play this MU more defensively though for the most part.
upB oos iirc is another tactic marios will use, and that's decent for misspaced things, but really risky overall.
FLUDD and cape will work if he's being dumb offstage like sapping his jump immediately, but if he dair stalls, fairs and saves his second jump for when he really needs it he can make it pretty confidently, imo Lucario's recovering options are really underrated, merely because his really strong options for clearing are offset by a mediocre upB. Lucario can also do some pretty nasty things to recoveries like Mario's, although I always say that gimping/edgeguarding with anyone besides MK is pretty hard to pull off correctly.
45:55/40:60 Lucario's favor imo, especially with stage pick. Lucario's going to have a holiday with stages like frigate, FD, YI, Castle Siege (lol FWK is going to post on this one obv.), and Brinstar (which I think is great in this MU for lucario), among some others.
Edit: Red's right, lucario fsmash and dair are habitual in nature, but good Lucarios know when to use them to make them much harder to take advantage of. Fsmash can be strutterstepped/slightly charged to make PSing/retaliating tough, and lucario has other options besides dair to take care of aggressive juggling patterns, like fair and b-reversal.