What should I do from a grab vs. Marth? Cargo-up to u-air tends not to connect for me.
Edit -- And any tips on how to play the Marth match-up in general?
Against Marth, i would generally u throw, do a FULL jump u air, and then use your second jump to jump towards him and quickly do your up b. If you do it quickly enough, you'll connect. You can't do a whole lot to marth from a grab, but if you do it right, you can actually rack up damage with your up b if you hit him with multiple hits. DK's up b has the potential to do 33 damage. Its not that difficult to do against marth, but you're probably not going to get all 33. Another option is to just full jump and giant punch him if you have it charged..
Getting underneath marth is something you wanna always try to do. Below him, he can either d air, do a forward b to slow his fall, or f air. Its unlikely that he'll d air because if he misses, then you have a free attack on him. If you stay somewhat closer to his back than in the exact center underneath him, you won't get hit by the f air, and you can do a sh u air underneath him. If he does his forward b to slow himself, then you can up b as you land which should hit him if your timing and spacing is right.
Against marth in general, you'll wanna dash dance a lot and don't let him draw you in with a dash dance because DK doesn't really have anything to beat marths. Just dash dance yourself. Don't approach with anything but the b air or the giant punch. Let marth try to attack you and try to just stay out of range and counterattack with a b air, but you have to be extremely quick, otherwise marth will just wave his stick around more and you'll land yourself in a combo.
Charge your giant punch constantly. It's a key move against marth because it'll go through anything marth has. Trust me on this one, in the beginning, the marth will generally be overconfident and just be waving his stick all around, BUT the first time you hit him with a giant punch, he'll be much more cautious. You don't want marth to be on top of you because b air and giant punch are the only real moves that can mess with marth and if he stays on top of you, you can't get away to get off a b air and you can't charge a giant punch. So hitting marth with a fully charged giant punch early is very important.
Another thing you can do to kinda get marth off of you is whenever you do a b air, you gotta fast fall it and l cancel and do a forward tilt. The marth will probably be dashdancing and trying to grab you or attack you right when you land, the f tilt should smack him away if he tries to grab, and beat his aerial moves and if he tries to f smash, your f tilt will cancel it out.
Ok....if you have any more questions, just ask them. I wrote enough to at least get you started. I could write a whole book on this matchup because i have a lot of experience in this matchup (even beat Mew2king's and Taj's marth). =). If you have any situational questions, i'll let you know what the best option is. Keep the questions coming.