Great guide! I just wanted to mention a tip I found really useful. Johnny Bravo's forward smash attack (use the right stick) takes a ton of health out of the few boss fights where they have a health bar. If you get a good lick in it will take out about a third of the bar.
In the Kevin, Aku, and final boss fights this came in real handy and if you have to beat the boss as a certain character you can just switch back to who you need to use for the achievement before you land the final blow.
This game is a fun and pretty easy 1,000 if you use the guide. It's a perfect weekend gamefly rental.