I would say that the matchup with Lucario is in Diddy Kong's favor 60:40
The main problem a Diddy has vs Lucario is his aura. Unless you get an early spike or gimp his recovery somehow, Lucario will consistently become stronger. To combat this, after you've gotten your first several combos in, approach with caution.
Another thing Lucario has up his sleeve is his down air. This pretty much makes it stupid to ever try and approach from below, and at higher percentages, it becomes a major pain. Unless you are very quick after your dash attack, for example, it wouldn't be wise to jump-> b/f air.
Advantages Lucario Has:
Damage Monger: Lucario thrives at higher percentages, and experienced Lucario players are not intimidated when at high percentages. So as his damage rises, approach with caution.
Range: The range of his forward smash far exceeds that of any of Diddy's non-projectile moves. Even the ftilt. The range of Lucario's Aura Sphere is also very large, and at higher percentages, could cause a major problem.
Diddy does have many advantages though. Among them:
Superior maneuverability.
Generally better equipped for most aerial combat.
Better approaches than Lucario but still good defensive game. (Assuming Luc doesnt hang back and spam b)
Superior Recovery
Musa acuminata
To Win Against a Lucario, i Would...
1) Try to gimp his recovery/go for early spikes. Even though doing damage is great, every attack Lucario gets that doesn't kill him makes him stronger. (Up to like 170-180 not sure which percent) So, take advantage of his up-b. It can't damage you, so there's no harm in trying.
2) Stay away at higher percentages. When Luc goes over 120%, try to hang back and rely on your bananas or otherwise low-risk strategies.2
3) Remember that Lucario's ground moves have a wide variety of attack delays. The forward smash is fairly slow, while the up tilt comes out quickly. Luc's capitalize on this, especially when figting characters that spot dodge a lot. If you are one of these people, the down and f smash can be a *****.
Stages:
Normally, my favorite cp is Delfino. This is risky choice against Lucario, since the platforms on the main stage aren;t THAT banana-friendly, and if you get wet in the part with those 3 pillar--islands and water below, Lucario will assrape you with his d-air.
PS: Not sure where to put Lylat. I think its pretty neutral for diddy/Luc
Stages I would pick are:
Final Destination
Smashville
Halberd (Though personally I hate it, others seem to like it)
Luigi's Mansion (If it's a cp)
Corneria (If it's a cp)
Frigate Orpheon (One of the sides of the stage has no ledge to grab, making Luc easier to gimp)
Yoshi's Island
Pokemon Stadium 1
Stages I wouldn't Pick:
Castle Siege
Battlefield
Delfino
Distant Planet
Pirate Ship
Jungle Japes
