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1. Beat Target Smash on all difficulty levels with 1 or 2 players.

2. Get Lucario to join your party in Subspace Emissary

3. Play 100 Vs. Mode battles.

As usual, you can earn Lucario by getting him to join your party in the Subspace Emissary.  If you are good at target tests, you can earn him by beating all difficulty levels of this mode. Remember, you have to clear Classic Mode two times on Very Hard, or once on Intense just to unlock the target tests. Thankfully you can bring along a friend to help you clear these challenging target tests. And of course, you can always just wait until you have 100 Vs. Mode battles under your belt. I don't know too much about battling him but he seems to be the new Mewtwo of this game. All I know for sure is you want to finish him off hard once he's hurt. His fighting spirits rise when he's in danger, and he will become more and more powerful a his damage rises.

That covers everything that I wanted to know about Lucario.  Thanks for the info.  I think that I am just going to unlock him by playing Vs. mode battles.  That seems pretty easy, especially if I play 1 stock games.  If I really wanted to unlock Lucario quickly, I would just do a Special Brawl.  If you put flowers on the characters' heads and put their health a 1, they will immediately die when the game starts.  This will make games really fast.  This is the best and quickest way to unlock the characters, if you don't want to do any real playing.