Without Aura and martial arts only... Diddy would take a rock, take lucario down and begin smashing the rock on lucario's face. Lucario dies with a desfigured face.
Chimpanzees are much stronger than humans and can take adult humans down pretty easily because of their massive strenght, speed of their tackles and weight. If Lucario is not much bigger than diddy then the task is much more simplified for diddy. Also, chimpanzees cause alot of human deaths a year because of how vicious they are.
And, depending on which martial art Lucario has, then it may be:
A) purely aesthetical or for non-fighting situations.
B) made for ritual fights against other practicioners of the style or
C) to defend yourself from other HUMANS. (AKA *ss kicking)
And I bet Lucario's fighting style is purely aesthetical because of 'making your chi flow' crap.
Lucario is another one of those characters that would get totally screwed if they fought in the real life.
Seriously? So many bad assumptions here.
A) Basically doesn't exist. Even stuff lik Tai Chi is a fighting art, just a number of people practice it for other reasons. Speed it up and it still works in a fight.
B) Yes, that happens, they're relatively rare these days, much more common are ones that are used as a sport. Many of the openly practiced styles like this have been adapted enough that they are usuable against other styles for self-preservation purposes.
C) Yes, this is the most common style HUMANS have. However you're making an assumption here, that just because it's built to fight humans means that it won't work against things that aren't humans. Honestly, that's mostly restricted to grappling only styles, because way too much depends on specific joint configurations and mass distributions. For Grappling it depends on how close they are to humans.
That said, striking styles are fine, in most cases, humans just lack the speed and/or strength to successfully execute them against animals. However, it's obvious that the fist-striking styles would work given the speed/strength required when we look at the fact that our weapons styles consistently destroy animals. A well-trained human with a sword>>>>chimpanzee.
Furthermore you forgot:
D) A style built to fight other Lucarios. Definitely a more practical variation on c, because Lucarios aren't exactly known for fighting humans. Still, this is highly unlikely, so...
E) A style built to fight a wide variety of animal form creatures. By far the most likely because this is what Lucario actually DOES, Lucario fights other "animals", aka pokemon. His fighting style would therefore be mostly striking based, and built to be as effective on various forms of opponents as possible.
BTW, "Chi flow" is just a mystical explanation for natural attributes, when you're pumped up, you have adreneline flow, when you strike from the ground, you get more force. While aura is a real force in the pokemon world, Lucario is a trained fighter reguardless. They may over-emphasize his "mystical" abilities in Brawl, but in pokemon, he's a balanced fighter in terms of physical and special abilities.
And "chi" certainly isn't the mark of a style built to show off, but if you're manipulating others' chi, it's a style that works only on humans, but there's concrete biological explanations why it works.
Lucario definitely doesn't have a have a human build, if you look at him, it's far closer to that of a big cat (panthers and such, not domestic cats). He also has extremely large legs, which means they're powerful, and based on the configuration they're built for leaping and short term very quick running. Whatever martial arts he has is obviously gonna be based on that.
Furthermore, he's got longer legs, that are obviously much more powerful (look at the muscular configurations, can you say, "kicks like a horse"?), and large protruding spikes on his paws, as far as natural weapons, he's definitely got the upper hand.
That right there's enough to guarantee his victory, combination of superior natural weapons, superior speed, and superior training (fighting type, remember?), and not techniques built to take down specific different creatures (like humans) but instead techniques built to take down animals.
If that's not enough, he's steel type. Good luck getting through his natural armor diddy.
Oh, and Diddy is smarter than Lucario because he can make high-tech stuff out of leaves, wood and fruit. Lucario talks with humans, becomes a pet ad doesn't afraid of anything.
That doesn't show tactical superiority, you're dealing with something bred to fight, vs. an inventor. And the thing bred to fight has shown that it can speak on a level equal with humans. Tactical superiority goes to Lucario.
BTW, I move for Diddy's "inventions" to be stricken, they wouldn't work IRL.
