Use Dtilt more often. It has a 50% chance rate of tripping and it's very quick, so you can hit with it multiple times. Utilize Ftilt too. It has massive range, good knockback and decent KO power. A good combo for early percentages is Dthrow -> Ftilt. Try using the headbutt if you predict spot dodges or rolls. Trust me, it's really useful that way, I learned so the hard way
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For the cargo, always ALWAYS attempt a cargo stage spike if you grab an opponent and you're near the edge (provided they're at a high enough percentage, of course). Another great setup is to Cargo Dtoss people off the stage, and from there on there are a myriad of things you can do, such as spiking them, Bair, or just plain toss them and walk a bit back to prepare for an Fsmash in their face (a rather situational strategy, but it works well enough).
Down B can be used on platforms as well if you tilt downward gently enough, though it only works well if you're fighting tall opponents, but it works wonders and it can surprise them quite a bit. I recommend doing this on Battlefield and Yoshi's Island (when the see-saw is low enough). Finally, be aware of the super armor frames around the beginning of Up B and around the middle of the DK Punch, and speaking of the Up B, you can move forward during the attack, but you can't move backward.
The one thing I really like about DK is that almost none of his moves (with the exception of Ftoss and
maybe Uthrow, I haven't really found the right moment to use it effectively) are useless.
