Use Fox. I've made attempts with nearly every character but Fox is the only one I've ever finished Intense with. I succeeded on my 3rd try with him, fighting Tabuu on intense for the first time with no problems at all.
Memorize the bosses' attack patterns (especially the one-hit-KO ones). Dodge attacks, then whenever there is an opening use Fox's front air attack (the helicopter kick). It does a very large amount of damage if all of the kicks connect, which is fairly easy to do since the bosses are so big.
Reflect things like Meta Ridley's smaller fire shots, it's easy and they do a ton of damage to him
Reflect Duon's rapid-fire projectile things (but NOT the blue lasers, those can't be reflected), and lead the slow white missiles back into him.
If Porky's "searchlight laser" is difficult for you to dodge, try using Fox's side-b to dash away from it
Make sure you are familiar with Tabuu's attacks and that you are able to dodge them all. You could consider going into the Subspace Emissary's Great Maze on intense, then fighting Tabuu there for practice.