I finally got him on the 4th on try, on hard mode, after learning his moves : )
The six character I choose was:
Olimar, Marth, Peach, Luigi, Sonic, Ganondorf
I just find my reaction time to his moves is too slow, or in other words he's too fast for me x_x He got me a few time with that grab move of his where you get trap inside two yellow side thing and then it throws you out. Pretty annoying : /
I got him with Ganondorf, sorta funny because how Ganon was trying to go after him before
How did you defeat your Tabuu? Any particular trouble?
Edit: Whoo unlocked all character : )