Thanks, Cors!
@Tiamat: Ha! Funny thing about Charizard--I never could use him well, first off because he's slow and heavy as ****. But secondly, I could never master the Rock Smash. Everytime I'd be in the air trying to do a side-B, half of the time I'd do an up-B instead (GCN analog FTL) and leave myself wide open to a boss' attack as Charizard just floats helplessly down to the ground.
Anyway, now for some Fox strategies! For one thing, I'm a neophyte at Smash and suck at Brawl (as my track record on wi-fi will prove). Moral of the story: If even I can do this, anyone can!
The Hands: Easy. Just use aerials, and air-dodge as appropriate. Master Hand's quick slap across the stage and the drill attack are your only worries here.
Petey: Even easier. Stand between a cage and the body and just up-smash (being sure to quickly jump when he swings a cage). Now when I fought him, I was at 116% damage, so I took no chances--I took the second method of standing off the side and laser spamming, in addition to dashing away from his jumps. It took a long time, but at that stage in the game (he was boss #6 or #7 at that point), better safe than sorry! I took no damage from him. Also note that after the firestorm temper tantrum, whenever Petey jumps, he *always* jumps twice in a row.
Rayquaza: Forget Fox's laser here; it does so little damage you may as well be standing there doing nothing. Just dodge (and air-dodge) as usual. But when Ray gets ready to shoot his big blue energy ball at you, use reflector to bop it right back at him! When his eyes turn red, and that random explosion happens on top of you, I used side-B to quickly escape. For the lightning (when Ray spins in a wheel), you have to shield immediately. Otherwise, just use aerials on his head and/or forward smashes on his body.
Porky: Ladies and gentlemen, meet Fox's achilles' heel. He is by far the hardest boss for Fox (at least for me as Fox), as there's nothing to exploit or spam. Lasers do slightly better than against Rayquaza, but still not enough. And he's capable of racking up major damage very quickly. Jump quickly over Porky if he makes a mad dash at you. Pray you don't get caught in the claw-pummel (and if you do, try to DI out of it--good luck). Dash through the spotlight, and for the laser, light hop + air-dodge x2. The few times when it's at rest (particularly when the Porky bombs are sent out), this is a good time to use Fox's best attack on Porky--forward smash. F-smash depletes that energy bar pretty quickly.
Duon: In stark contrast to Porky, Fox is GOD against Duon, and this matchup is the #1 reason I recommend Fox for BB-I. For one thing, when Duon charges you, Fox is one of the few characters who can clear the beast with a double-jump (i.e. without needing an up-B on top of the double jump). Against Big Blue, when he lurches forward to combo you, let him in close, then jump backward while air-dodging, and you should clear the whole thing. For the bombs, try to find a gap (there normally is one, even on Intense). The only other moves by Big Blue will only be a problem if you're close, which you shouldn't be--Fox's laser does decent damage and should be used at all times while Blue is facing you (except if he's about to charge).
When you face Mr. Pink, that's when the real fun begins! xD For one thing, get up nice and close. And if you see it reeling back and getting ready to fire out those pink lasers, put on Fox's reflectors. If you're close enough, the pink lasers will be reflected back to Duon dealing MASSIVE DAMAGE! If you get the blue laser, though, er--that's the only attack that pretty much always gets me. Double jump over the first one, air-dodge the second one, and hope your shield lasts through the third one. But yeah, I pretty much always get hit by that (pray your damage % is low enough to survive the hit--or position yourself backward so you go flying *into* Duon and are thus buffetted by him). For the homing missiles, jump over and/or air-dodge--or if you're feeing daring, jump over and behind Duon to guide them into him (for more MASSIVE DAMAGE), but it's very risky. Only do that if Duon's pretty low on life.
Galleom: Kind of a case of "****ed if you do, ****ed if you don't." If you keep your distance, you make yourself vulnerable to his missiles, which are tricky to air-dodge because you don't think they're going to hit you--but they do. Get too close (which is an otherwise great way to avoid the missiles), and you set yourself up for the uppercut punch, which comes out fast and is hard to prepare for in time. So stand medium-length away, get used to roll-dodging (which I'm never good at, BTW)--and really hope you don't get this guy after the first five because he gets ridiculously fast and furious. Against Galleom, Fox's laser does the most damage, so fire away! Smash attacks also work very well too. When Galleom turns into a tank, double jump--but if the tank doesn't move but instead fires missiles, just add your up-B to the double-jump, and you should clear it.
Ridley: Pretty elementary. Use aerials when he's just floating there doing nothing, but always be wary of Ridley's somersault attack. Also, make sure you're not too close in the event of his roaring wind attack, which does surprising damage if you're touching his mouth when he does it. But fight against the wind and get in as many free licks as you can! When Ridley flies off-screen to the side, walk a step or two, then double-jump, and as you're coming down, Ridley should by this time fly in above you, narrowly missing you. (Air-dodge if you want to be safe.)
Meta Ridley: Okay, when I said that Fox was God against Duon, I was wrong. Meta Ridley has never been so easy as against Fox McCloud! Use aerials as usual for fighting and air-dodging as usual when MR is attacking. But when MR comes in for a round of fire-bullets, get ready for more fun! Get up close to him and put on that reflector (it works even better if you use it while in the air) in order to rack up--yep, you guessed it--MASSIVE DAMAGE! Moreover, I hear that the reflector works against the giant fireballs too? If that's the case, then when MR gets on the back end of the ship and gradually drags it down, just get in front of him and reflect to teach him a lesson (if it's true anyway--I haven't confirmed it for myself yet). In general, during the drag-down attack, I just play it safe and wait on the front end--double jumping at the end to ensure safety until the ship comes back up again (up-B on top of that if need be).
Tabuu: Any battle with Tabuu is a lesson in the art of the dodge. By this point, you should know what to do. Double jump when necessary, and if it makes you feel safer, use the up-B to get over attacks on the ground. For attacks where Tabuu is stationary (i.e. electric circle attack, ground pound), dash quickly out of the way. Then from the safety of a far distance, turn around and shoot lasers. For the golden bracket, air-dodge *immediately*. For the lasso, dodge before you even see it coming (yeah, I know). And finally, for the most dreaded Off Waves, you just have to time it right--there's no teaching it. Practice on SSE. Down-shield just before that red line touches you--and do so thrice (I find that the first ring is the hardest one, FWIW). Lastly, take every advantage you can to get in as many aerials as possible whenever Tabuu is just free floating up there.