The Lucario I play against often uses backrolls and other very safe tactics, using superior aura spheres and aerials to keep my Pacman away and control the zoning game. The few times I "get in", Lucario uses counter to force me to think about my approaches (Pac-Man's grab is underrated honestly... but very unsafe on whiff. Especially against a high% Lucario).
Lucario wins in the zoning game, hands down. Pac-Man's fruit are great, but Lucario spams more micro-spheres and simply controls more space. It is Pac-Man who needs to be the aggressor in the matchup. From the get-go, it feels like Lucario is "in control" of the game.
From there, getting Lucario to 80% is easy enough. Beyond that, the game becomes much harder. Lucario's hitboxes become insane (side-B as a zoning tool, wtf), Sphere Spam is stronger, smashes hit harder, and his down-B can KO 90% Pacman in reaction to me throwing a cherry. :-(
So it is a little bit about getting outplayed by Lucario, but it feels like I'm on a clock vs him. If i don't actually finish the job, Lucario can take advantage of his massive recovery to make his landings unpredictable (at 130%+, Lucario can recover from off-screen left and land on the right-side of Final Destination. No joke, its huge). So its very hard for me to actually land that killing blow against smart players who mix up their landing options.
My typical "gimping" strategies don't seem to work. Off-stage Fair-Fair doesn't cut it, you actually need to deal a solid knockout blow vs Lucario.
Thus, I end up facing Lucario until like 160% (when Bair finally can solidly kill), and end up losing my first stock, and take like 40% or 50% on my 2nd stock before I KO Lucario's first stock.
If I can get fair-nair off-stage combos down pat, and if I can get more Bell-Smash combos set up... maybe I'll do a bit better. But as it stands, I think Lucario is my greatest foe (tied with Rosalina).