well, you guys seem to love his dancing blade so i'll go with it for a while.
i've discovered that you can have three variations on the timing. there's the normal one, where they just flow. this is what most people use. then there's a quicky where he just dashes and smashes. this takes timing also, but i've done it. (i actually figured this out from a comp... yeah, i feel embarassed somewhat.) you have to press the buttons just a split second faster and he just throws it all out like crazy, but it works best with all over b. and then there's a slower one, where you press the buttons just a slight bit later than usual. this seems to work with non over b combos. (i.e. overb, downb, downb, upb, etc...) this is helpful for timing out your hits and whatnot.
several of you are just talking about "i like to spike." well, his spike is good, but it's sort of difficult to connect correctly with it. the best way i've found is to keep his japanese *** over the ground and hit with the tip of the blade right at the start of the attack. you should stay over ground because the spike has lag like you wouldn't believe on it, so you could easily kill yourself on accident, not to mention (like most other quality spikes in the game) it knocks at an angle instead of directly down.
combos... well, i don't use deadset combos, just whatever flows. most of my comboing is in the air as well, since he seems to love launching people up there. i just over, back, and up a them to death. (also throwing in a few dolphin slashes.)
and on to the dolphin slash. if you watch carefully when you do it, you'll see this little orb or circle of light at the tip right before he goes up. if you can manage to connect with this little circle of light it causes the most damage and has the most knocking power. hope that helps someone out there somewhat.
abuse the **** out of his cstick over smashes. that'll surely put a smile on your face and a grimace on your enemies'. as mentioned before, they're faster than a thirteen year old boy who just learned how to whack off and they have a pretty good range (over and to the side.) ledge guard with this and tap b shield breakers.
and the shield breaker. ah, what a fun move. you can ledge guard people to death with this. if you can manage to connect with the tip, it'll out prioritize most other recovery moves (but if you whiff and hit with the middle, you'll both end up flying.) a good way to guard with this is to just tap it. when they come up towards the edge, get your timing down and just tap b to connect with the tip. they'll fly off, then come back. keep just tapping it until they get some good distance, then charge it and keep it up. (obviously this is only useful if you're playing one on one or your other opponents are busy on the other side of the screen.)
countering is fun. all marth players will usually agree to this. if you can get your wave dashing down, you can wd into an attack while countering, throwing your opponent off. (i'm still working on just plain wding, but i know this is a possibility.) if you can get really skilled with this, you can disrupt enemy combos (both used against you and just butting yourself into someone else's business.
fun things i know to combo.
1. unown. there may be better things to do than just float down out of the sky and go counter happy on a bunch of pokemon, but i don't really care. if there's no through them this'll at least save you some time and damage.
2. bobombs. heh, yeah. all it does is make them explode above your head, but you never know when that may come in handy.
3. another counter. wierd, but it can be done. best way i can think of is to go to a team battle with one marth on each team and at least one falco/fox on the other. you stand in front of the other marth and his falco/fox shoots one shot. you counter that and then the other marth counters the counter. it may be possible to counter a countered counter even. have the teams set up as two marths and the other marth falco/fox. follow directions as before, but this time have the two teamed marths standing one behind the other. when the second marth counters the first marth's counter, have the third marth counter the countered counter. wierd, but fun...
now more strategic uses for the counters. obviously the best one is anti ledge guarders. if you float down next to the enemy and counter, they'll get knocked away leaving the ledge more or less open for you to either jump again, up b, or just grab on.
or, counter over and down b's from falcon and gdorf. these moves are relatively fast and if you can manage a counter off of them, it'll normally throw the user off a bit so you can go and start some aerial fun.
projectiles, whether "natural" or from items (event the items or capsule/egg/crate/barrel themselves) can be countered. useful if you can manage to deflect a fully charged samus blast into someone above you. but be careful of shadow balls: unless you can manage to get slightly below it before you counter you're in a good position to get hit due to its motion. (the item carriers will be destroyed when you counter them.) ray guns, fox/falco blasters, and ***** super scope shots will merely disappear when you hit them but if someone's in front of you (i.e. the shooter) they'll get hit by the swing (and the swing will block two or three fox and super scope ***** shots.)
well, that's all i can think of off the top of my head again. as soon as my brother stops playing that stupid simpson's game i'll go back and mess around some more.