Dash dancing in neutral to punish whiffed attacked with either A) Dash Attack or B) USmash and SHFFL Fair are your best friends to land a hit. DownB cancel is good for approaching as well, but you risk missing the attack and burning a charge, so I typically use DownB cancel for combos. And example would be (medium weight and fast fallers at higher percents) a ledge-hopped Fair to counter your opponent's edge-guard, then DownB cancel into either A)UTilit or B)FSmash-slightly charged DSmash, depending on character and percentages. Another good use of comboing with DownB cancel (and, imo, a big "**** you" to your opponent lmao) would be something like (lower percents) Dash-attack>FSmash>DownB cancel DSmash> (if you have a second charge and follow their trajectory correctly) another DownB canceled DSmash/FSmash or an USmash/UTilt for juggle options. You can also ASC Lucario's USmash in 3(?) positions: standing, as he starts rising with the USmash to follow your opponent up, and right at the top to be positioned slightly below them. This is great for platform mindgames/combos. A very quick kill option if your opponent doesn't expect it is DownB cancel Jab1>DSmash, and DTilt to Aerial SideB is a good option as well. UpB cancel>Nair is a prominent kill option as well as using an UAir if you sweetspot it. Dtilt>ASC>Nair and DThrow Nair are also possible kill setups. Back-air is a strong option, as well.
Also, when you get to this point, ASC EVERY aerial if you don't DownB, UpB, or SideB cancel it into something. This makes insane Fair chains possible. First hit of Dair also ALWAYS cancels into SideB.
This wasn't much, but it's all I can think of without any specific questions, hahah. Hope I helped! If you have any questions, I'll try to answer them to the best of my ability.