DK's bair eats through fireballs, allowing him to easily SHFL bair right through your fireball camping, and get to you...
And DK controls the direction of his upb, so an expert DK knows to point in the opposite direction after getting caped, making him use what little of his upb he has left and come right back, like a boomerang, allowing him to still make it back to the stage. So not only will you have to cape twice alot of the time, but the spacing you need to land the cape while avoiding the reach of his spinning arms is strict.
Reverse giant punches are dangerous if you aren't careful, since they can do it at any time after a bair or pretty much anything. And 8 or 9 swing charged punches will kill you at any time when your in moderate percentages, which you'll be in most of the time since DK's attacks do great damage.
DK's ground pound (down-b) will break your shield easily, and they like to use d-tilts to make you back off when your putting on the pressure (and the added chance that you might trip and they get a chance to attack is also a plus).
When your above him, an up smash will do great damage and can KO at low percentages. They usually do this when your on a platform, which they usually wait for a second, then when you try to air dodge or something because you think you see it coming, you get punished. The ground and platforms cancel air dodges, so airdodging before you hit the ground defeats the purpose of dodging, lol. But if there isn't a platform, they'll try to pull a sliding up-smash, hoping you won't see it coming. Oh, and DK's u-air is fast and strong, just like his bair, a laggy yet huge and strong fair, a quick dair spike, and an ok nair give DK a pretty good air game. So he DOES have the options to combo break out of our uairs combos if given even the slightest chance.
Getting stuck under the bottom floor of Luigi's Mansion by DK's ground pound... really sucks.