This fight seems a bit one sided, again. Diddy has technology, but Lucario just kills him in everything else. Even without Aura, he has Extreme-Speed, Double Team, Close Combat, etc.
BUT I should probably go more in depth to prove why Lucario wins this hands down. Which disheartens me, because I think Diddy Vs. Ivysaur would've been the MUCH superior choice to this. Or Lucario and Power Suit Samus.
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1. WEAPON- Diddy has his popguns, jet-pack, orange grenades, and if at all possible, a guitar that can somehow manage to generate shockwaves. Lucario has no weapons, but doesn't need one; he's a fighter with a mastery of many martial arts and uses them to defeat other creatures far more intimidating than Diddy. Even Diddy's arsenal is too slow or cumbersome to catch up with the constantly dodging Lucario. This one goes to Bluey.
ADVANTAGE: Lucario- His body IS the weapon, and the best one you can master at that.
2. PHYSIQUE- Diddy is a tiny, weak, and frail chimpanzee. Granted, he's speedy, but he has little else going for him in the endurance department. But Lucario... I mean, really? Even if Diddy manages to land shots with his ZOMG PEANUTS, they're either going to tickle Lucario or just moderately tick him off.
ADVANTAGE: Lucario- This match is not going to end well.
3. ARMOR- Neither fighters wear armor, meaning it'll take a mere few blows to finish the foe; however, Lucario can do it in one hit, whereas Diddy will probably need to land more than THREE at best.
ADVANTAGE: Lucario- His power is matched only by how unfair this matchup is.
4. SKILL- Diddy is smart and has crude technology. But Lucario is a superhuman athlete that could easily keep up with Diddy's swiftness and technology.
ADVANTAGE: Lucario- Honestly, this makes me, as a Diddy Secondary, cry.
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So yeah... in conclusion, this match will end only with monkey blood scattered.
Whoa, you are seriously overrating Lucario.
WEAPONS: Diddy's weapons wouldn't work on the real world, and Lucario would not be able to use energy attacks or aura, so there are no real weapons here.
PHYSIQUE: Lucario has low defense and stamina. He will feel a moderately powerful attack AND a strong attack will probably leave him very damaged.
And chimpanzees are not frail little creature. I dare you to fight against on and see if you last for more than a few minutes. Chimpanzees are 3.5 times stronger than us humans. Lucario is smaller than a person.
ARMOR: again, lucario has low stamina, defense and has a small and frail physique, and he dies easily in the games too. Hell, a POLITOED (a frog) has more defense and stamina than him!
Chimpanzees constantly fight each other and survive sumersaults and blows from each other in their environment.
MOVEMENT: Lucario is not a superhuman athlete. His speed is above average but it is nothing to be very proud of. His speed is the same as a Poliwag's speed. Woah, that sure is surprising!
Diddy is very athletic, can make great jumps and can swing from platforms easily.
ADAPTAVILITY: Lucario has no real advantage on any real battlefield. Diddy could easily overpower him if they fight on the jungle, on a confusing place or a place with multiple platforms and places to hang in.
POWER: Lucario has a high attack stat, but it still is not broken. Diddy is 3 times as strong as a normal human and the speed of his attacks add to the already enormous strenght.
SKILL: Lucario is more skilled than Diddy because of his fighting styles, but, were they created to fight against angry simians? Or were they made to fight against other practicioners of the same fighting style or to defend against robbers with knives? If they were made for the latter, then superior skill will not matter.
ATTACKS: In a realistic fight, there are no peanut popguns, propulsion devices made out of barrels, energy attacks or your body suddenly transforming into metal to attack the enemy. Lucario still has physical fighting techniques, but those are techniques like Karate chop, close combat or normal stuff like that. Diddy has his simian grapple moves and tackling abilites. Noone has anything special, really.
If Lucario could use his normal techniques, then he may have a chance, but not here. This is a 'REALISTIC FIGHT' situation, not a 'TRUE TO THEIR GAMES' fight. Without his abilities Lucario is screwed. And even with them Diddy could still put a fight.