Any hope Meloetta had of ever becoming OU is ruined by Aria form. Thus, the only set she can run viably is a transformation set. I had the EVs worked out perfectly in my old Dream World analysis thread
: 224 Att / 84 SpA / 200 Spe
Her Close Combat hits about the same as Lucario's and the Sp Att EVs giver her a decent chance to OHKO Skarm with Thunder after Stealth Rock damage. Btw, user her on Rain teams; Thunder is kind of necessary.