I main Lucario, 2nd Mario/Snake. Snake is a completely different playstyle, and also favors different stages (overlooked aspect I think). If my opponent is afraid of Lucario they'll ban a bunch of small stages. I'll counterpick something like Norfair/Skyworld/DL64 and go Snake if the matchup calls for it.
Beyond stages, I think Mario actually covers what I consider Lucario's bad MU's. Squirtle, Metaknight, Mario, Ness, Lucas (this isn't that bad for Lucario), or spacies that I'm having trouble controlling. His crouch cancel game is absurd and he has a significantly better neutral with Fireballs. Like Snake you have to play far differently against him than Lucario.