By the way, for ROB, the only way he's going to kill you below 140% is with a glide toss > Fsmash or with the <<top part> of nair. Don't come down from above him, try to stay beside him at all times because the top part will kill you a lot earlier than the sides.
Anyways, a good ROB won't spam Dsmash. One thing that's annoying is if ROB spot dodges to dsmash when you ftilt him and it hits you because of your stupid *** hurtbox. If they are dumb enough to do this, short hop a headbutt right on him. Just long enough to beat his spotdodge and it will plant him if he Dsmashes.
For some DK tips: Grab a lot. Shieldgrab approach is useful. Some good DKs to watch are ripple, ook and bum.