What did you use to access Brawl? And what mods do you have (minus character mods)? Also, is this a recurring problem or did it happen once? Did you try and play as Sonic again? Because the Wii itself might have overheated. If it's a disk, check for scratches.
well, i tried it 4 times and it froze everytime, then i removed my smashbros_sound.brsar and it worked perfectly so i think i fixed it. But now i need to figure out whos SFX froze it -_- lol. Thx though for the help