I'm a Lucario main, so I can tell you what you need to know about him.
For starters, Lucario is a deceptive character. He doesn't look all that impressive outwardly, but once you really look into him, you start to understand that he's actually incredibly effective.
Lucario has some of the best defensive play options in the game, and can change to offense without losing his rhythm. What's more, he has some of THE most amazing priority as far as disjointed attacks are concerned, since all his hitboxes linger for much longer than sword users not called Ike.
KO power is not a problem, since at around 100%, he has more than average KO power on top of his already excellent frame times and defensive options.
Also, a good Lucario player is harder to edgeguard than you'd think. On many stages, they can wall cling and then immediately walljump back onto the stage while dodging or attacking. They can use reverse-double team to get past gimping attempts using projectiles, and they can throw aura spheres at you while you're waiting at the ledge for them to throw off your timing.
He also has incredible edgeguarding ability himself, thanks to his Fair and Dair having such awesome lingering hitboxes, and also the fact that his throws have very little ending lag, allowing him to pursue and gimp very effectively over the edge.
I believe Lucario should be mid high tier or bottom top tier, but since he's an unpopular character, not many people attempt to play him effectively or understand how his strengths work. For me, I find him to be a top-tier killer. He has 0>80% chain grabs on Snake and Wolf, has hitboxes that beat Marth, Metaknight and Pit, and has the defensive options to match evenly with ROB and Toon Link.
As a Toon Link against Lucario match up, I'd suggest not using your bombs or arrows TOO much, since a good Lucario player will start using double team to advance on you or even attack you in the case of the boomerang. Don't try to hit him with up smash when he's above you, since his Dair beats that. Not sure about up air though.
Lucario can't chain grab Toon Link and generally Toon Link beats him in the air, especially backwards. Aside from that, he outranges and outprioritises you with all his basic aura attacks. Don't think you can punish him when he does an Fsmash or a Down Smash, you'd be surprised at how small the ending lag is.
I'll second what everyone else here has said and tell you to focus on his one obvious weakness: his recovery. Don't use Fair to edgeguard him, use Nair or Bair, since he'll just Fair you as he's coming back if he sees you trying to use Fair. If he gets below the stage, follow him down quickly and try to knock him off before he can edgehop back on, but don't go overboard or you won't be able to recover yourself.
Also: down smash slips past a lot of Lucario's ground hitboxes. It's faster than his Ftilt and has about the same range, and it goes underneath his jabs.
And yeah, stand still to block his aura spheres rather than blocking them with a shield.
