I'm still playing this, I beat Classic on Intense and cleared some Adventure on Hard, I did All-Star on Very-Hard, that was annoying. So after I did all of that I went against Lv.9 characters, Wolf Wolf and some other character, I think it was Lucario, they kept stealing the Smash Ball yet they managed to always miss me. Except Wolf, his Landmaster is hard to avoid but at least it doesn't stay on-screen for as long as Fox's. Tabuu was loving annoying as hell, I can avoid every attack except when he uses his butterfly wing attack. Every time I tried to dodge it my character was insta-killed, so instead I decided "Screw it! I'll beat him on Easy then go up as I get more skilled"
The Game isn't very difficult.