Well, Lucario can really juggle Snake around at first. It's pretty hard for Snake to approach. But, if the Snake uses defensive tactics, he can destroy Lucario. It's pretty hard for Lucario to avoid being camped.
Also, Snake can really edgeguard Lucario quite well. All he really needs to do is keep the up smash going. Lucario can't do anything about it. But, when Snake gets knocked off, he can do what he pleases because there isn't much Lucario can do when Snake uses his cypher.
I guarantee that every Lucario player will say that he/she will have a lot of trouble getting around well placed grenades. Hence why I said that camping Lucario with Snake is a great choice.
But, I don't like camping so I get myself beat up by all of Lucario's attacks.