So, someone ban vudu. It seems he's provoking bots. Finally, the pieces of the puzzles are falling in place.
I'll also add some tips in a moment.
Edit: I wanted to sneak that in there before bot was banned, but was legitimately going to post in this thread when I saw it was bumped.
The best way to fight Taboo is simple: Not on Boss Battles. It's quicker to get a ton of experience playing him in adventure mode on intense, up until you can kill him with one character consistently, where you've learned the timing to dodge all of his attacks. When you do that, it's merely a matter of making it to him on Boss Battles Intense.
I'd say the same thing for other bosses, but some are tricky, like Rayquaza and Duon. Of course, the most important thing is not to get hit! If you can avoid getting hit, you'll be able to make it farther. Rayquaza, if you're careful, is easy to dodge, just don't get over-agressive. Quick physicals, like Ness's down tilt, can tear off chunks of health faster than anything else. Experiment a few times with all of your character's attacks to see which ones do the most damage and allow you an easy way to dodge whatever attack might happen.
Duon is more of a problem, a place where Ness also cam in handy, because it's difficult to hit him without getting hit back. As Ness or Lucas, you can absorb his energy burst shot that makes a quarter or half circle, depending on how he charges. Projectiles can work for some characters, but most should just run in, attack a few times, and then escape before the next attack starts.
Porky is another tough character, suriviving him can sometimes be a matter of luck. When he's moving after you, and his steps are attacks, jump over him and use projectiles. When he's standing still, attack as quickly as possible with a strong attack. He's one of the bosses where you'll almost always take damage, because he's built with a few unavoidable attacks, which is just terrible.