ah, the DI.
I don't bair against marth all that much, I know its counter intuitive, but most of my air attacks on marth are nairs. It's complicated.
When I play against marth's, I use ftilt like I use bair against everyone else. DK's range on his f tilt is longer than anything marth can throw at you, as long as you time and tilt right, you can hit marth out of or when he's lagging from anything. Usually, if I catch a marth slipping, I'll jump in with a nair to dtilt to ftilt combo, or I'll simply punch, the move that trades some of the ftilts range for like twice its power and 3 times the knockback.
Marth is pretty fast, but dk can be fast as well if you learn to wave dash and waveland like a pro. Mexican and PKMVodka have proved it. Also, no one watches out for dB.
Part of my new style is watching to see if the marth I'm playing against jumps a lot of not. If he stays on the ground for certain things *which any respectable marth wouldnt* I'll try (a maximum of three times) to surprise him with a dB. It's worked before.
something that few people are able to predict is DK's fair, which can lead to an uair combo if the marth is one who stays on the ground a lot. It can kill if the marth stays in the air a lot, specially on small stages.
Also, I've been working on my recovery with dk. DK has a weird teching thing on the edge. . . almost as weird as mario's wall jump from up b on some stages.
