"Sadly, I have not finished the Boss Battles on Intense yet.. I can't find a good character/strategy to use.."
Eh.... lol I used Luigi for Intense. Relatively quick, does his judo chop a lot faster than the previous game, and has extremely good recovery. Just watch out because the game will apparently get PO'ed if you get to the 7th or 8th boss on Intense.... and it really doesn't like you past that... all the bosses get insanely fast so.... learn to dodge. The reasoning: I guess they really want you to earn that trophy/they want to drag it out because for every 6 dodges you do, you can throw in some cheap shot if they're all over the screen and smack like a pixel worth of health off them. Fake difficulty? I'd think so.
I only use-
SSB: Mario exclusively
SSBM: Mario exclusively
SSBB: Luigi exclusively (because they screwed up Mario's Down+B)