Link is by no means an opponent to be underestimated, except when he's off the stage.
However, on stage, his range is pretty good. Unlike Toon Link, his first slash on his forward smash is enough to send you flying, so he'll only do the second hit as a mind game sort of thing. He can really close the space between you two with his boost smash. If you haven't seen the range on it, go look up a video. While it looks scary, it's really not that bad after you've seen it once or twice. In fact, if you see it coming, Link's a sitting duck for an Aura Sphere or f-smash if you're fast enough. His up smash is pretty powerful in general, and it doesn't have issues keeping you stuck for all three hits until very high percents in which you probably should be dead anyway. His down smash is powerful as well, like a middle ground between the non-tip and tipped Marth down smashes.
Link also has jab cancel combos, but if you're paying attention, he most likely will not be able to follow it up (f-tilt or f-smash are the follow ups I can recall at the moment), so you should just be prepared to eat the third hit, or roll out of the way. Also becareful, his up-tilt can juggle you if you just fall back down, and f-tilt hits behind him on the start up swing. Down tilt will spike you if you're hanging on the edge, but you shouldn't really be on the edge that long anyway. You'll also have to watch out for Link's z-air (the clawshot), it has pretty long reach and two disjointed hit boxes if I recall correctly... It's used during approaches AND retreats because of it's range. Though since Lucario isn't THAT big, you'll probably be able to shield it or air dodge it just fine.
His projectile game can get annoying. His arrows are rather fast (though at higher percents, I believe aura sphere will past right through them), and his bombs, while not as big as Toon Link's in their explosion, have higher knockback, which can get annoying. The Gale Boomerang can be stopped with an Aura Sphere, but it's pretty fast and some Link's use it for Edge guarding, though it doesn't seem to be an effective tactic on Lucario, since it mainly shuts down poor recoveries like... other Links anyway. Link players can also arrow cancel, which basically allows them to fire arrows VERY quickly but at the minimum range (which isn't that bad actually). However since the arrow arcs low, you can jump over it easily. Link has a huge variety of techniques with bombs, some of them being able to smash attack while having the bomb in hand, so don't think you're safe from smashes just because they have a bomb in their hand. Also try to use the Gale Boomerang's ability to bring you closer to him to your advantage and not his. Link's spin attack on the ground is somewhat of a punishing move, and while it's not likely to KO you right off the bat, it does have mean horizontal knockback, so try not to let him hit you with it.
In the air, you should be wary of what Link can do, but certainly not afraid. His up-air is a powerful attack and it's hard for me to tell if you can trounce it with down air, but because it's slow you can probably avoid it with an airdodge. It also lasts quite a bit, and Link has to use it high up in the air or he'll get landing lag from it. His down air is a killer, a very powerful killer. It doesn't insta-fall like Toon Link's, so it's much easier to see coming, so just becareful while you're trying to combo him from below using Lucario's up tilts and up airs. Link's back air has 'ok' range, and it is a quick move, though since he's kicking you, feel free to kick him back with a disjointed hit box. Treat his nair like you would most sex kicks. His forward air can kill you if you get hit by it, but it's pretty shabby on range as well, and it's not very fast on execution (I think it's start up is similar to our back air but maybe a bit faster?), and it has multiple hits, so just kick him with fair or something before he can get it started.
The main things you'll probably see from Link are projectiles, followed by attempts to launch you into the air and then follow up with aerials, or simply to stay on the ground and attempt to kill you via smashes. Most of their damage racking will be a result of projectiles, jabs and tilts, and if they can, smashes. Up smash and forward smash deal quite a bit of damage, and forward smash can connect both hits at low percents. Link's aerial game isn't a big issue if you play it cool, because your aerials will beat his, almost by speed and priority alone. His ground game isn't bad at all, but I wouldn't say it's better than ours. We can probably rack damage faster than Link can, and we don't really "have to." Get Link off the edge and slap a few fairs, or a dair, maybe even a BAS, and well he cries explosive tears that turn into fireworks. His tether recovery is mediocre, and while his spin attack has high priority, it doesn't shield him completely. In terms of him trying to gimp you, he might try to run off the edge and fair/(dair if they're feeling courageous) you, but he'll probably prefer to just wait on stage with some projectiles, because they don't want to risk being gimped themselves.
That's the input I have, feel free to point out any mistakes you see.
