2'nd for the win!
Source: Because my brother mains Lucario. DX
Will edit this post if I think of anything more.
I think that the more important thing to remember about Lucario is that you can't win an aerial fight with him. His aerials are better than ours because of their slight disjointedness, and don't try to come up under him with an Uair because if he predicts you, he'll Dair you in the face. Likewise, all of his others are better than ours. Stay out of the air. Our ground game > his ground game.
If you are eating a barrage of Fairs, and he is pushing you to the edge with them like a Ken Combo of sorts, then DI towards and below him. This will get you behind him so you won't be trapped in his manslaughter and you could punish if you think you can, or go for something else.
If he's coming down from atop you with a flurry of Dairs, and he is far enough away, thunder him. I don't think he can stop and DI away in time to avoid it, and the Thunder lasts too long to airdodge it.
My brother likes to charge an aura sphere as he's recovering back to the stage and launch it at full power right at the edge to get you away so he can recover. It's annoying. And it's ESPECIALLY annoying when he spams it. I like to jump over his ballz and wait for him to stop spamming, and then he approaches me when he is fed up with me camping him with Tjolts. But that might just be his poor playing. Also, be aware that when he's charging his AS, it can damage you and possible trap you. Be ready to jump/powershield it if you get trapped and he rolls, because he will probably fire it.
His jab is relatively slow. if you manage to shield grab him out of it, which is relatively easy, make sure you try to thunder setup like Zero suggested. I think its a very good idea to kill with thunder. Unlike other characters, Pika has to kill Lucario fast and early because he gets stronger. And pika's light weight is bad for this.
It's also very important to know that if he is far away enough from the stage, EDGE HOG HIM. His Uspecial does no damage, so just hang there and wait for him to die. If he trys to use it near the edge, jump and Nair/any aerial him. He will go right back off. Also, if he is recovering from above, THUNDER. If he extremespeeds around or over it, punish him out of his special fall. If he airdodges, then get away. You will most likely eat a Dair again. If he is forced to use his Uspecial, move in to punish. He also has a bit of cooldown time for hitting the ground during his Uspecial animation, so just go up and Fsmash or grab him lol.
If you get trapped in his Utilt, mash your analog and C stick like mad. He won't stop his madness until you get out of it.
I would not suggest rolling around Lucario either, because a lot of his moves cover a large area, such as Dsmash or Utilt, or even his Nair, because he will get you. If your gonna roll anywhere, i suggest rolling away unless you are sure he won't hammer you with the Dsmash or something stupid.
Also, lots of Lucario's smashes are a little delayed, so keep in mind that spot dodging might be better if you are a little delayed. His Fmash has slammed me countless time because I spot dodged too early. Also, his jab is not good to spot dodge either.
Recovering with skull bash is a bad idea, because you will get punished with yet another Dair to the face. Use quick attack to zip around him, he will more than likely not hit you. Now the thing to watch out for is the AS off the stage. When you are recovering, always be watching him because he will probably try to slam you with AS from the edge. This is certain doom for Pika.
I have fought Lucarios that, when recovering from below the stage, will cling to the edge of the stage and wait, then jump to recover. If this happens, then just Tjolt him. I think I've gonne two or three good gimps from this because of his punishable Uspecial.
If you manage to FF Fair Lucario, I would suggest an immediate grab or some tactic that is just as fast. This is because my brother ALWAYS utilts me when I try to utilt him straight out of it. It comes out faster than our Utilt, and is not fun to be hit with.
I would reccomend Usmash out of the Fair, but looking at the hitbox frames (Lucario's utilt hitbox comes out on the 5'th frame), I wouldn't do it unless you are sure he won't utilt you. I just was hoping it would be faster so you could set up for Thunder at higher percentages for the KO or something.
Also, I like this post from the original thread. Thanks a lot Mister_E!:
Oh dear Lord. I hate fighting Lucarios.
Lucario is naturally a beast at spacing. His aura will shoo you away if you try any one of Pikachu's many approaches.
There is 1 decent way to approach. It's too fast for Lucario and really any other character as well. QAC, QAC, QAC. Oh yeah, and more QAC. QAC again. Then QAC some more.
The spacing and timing problem that is hard to overcome against Lucario, you can make up for in blistering speed.
Also it should be noted that your t-jolt cancels out his small-medium sized aura sphere, but not his larger ones.
In the air, it's again all about spacing and timing. He has more range than you in the air.
Don't go all ferocious DBZ-style aerial combat on him. You'll fail every time against an experienced Lucario.
Instead, try to drop down fast and mindgame him into thunder or d-smash.
If the Lucario is very aggressive, and most Lucarios are not, then d-tilt, t-jolt, and grabs will do wonders for you.
Fortunately, on the ground you can FF fair combo him easily if you can just initiate it by hitting him with the FF fair. But his spacing is naturally godly and it will require some advanced mindgames and great timing.
Lucario > Pikachu
(More to come later definitely. When i think of it.)