you're samus. you aren't going to be comboing DK.
you need to control space and apply pressure with missiles, and use jabs, bombs (they work to an extent; watch out for DK's that will hit you with an Up-B when you hit him with bombs. you need to properly space them), dtilts, dsmash, and ftilts as your primary source of ground based assault. you can use nair and bair a decent amount, but don't try to beat out DK's bair. use dair to edgeguard him since DK has awful horizontal recovery.
things to watch out for:
grab. DK can't cargo uthrow uair combo you, but samus kinda sucks at getting back down to the ground, so chances are he'll be able to get you with at least one upair before you get back on solid ground.
taunt. DK has the best taunt in the game and should be properly respected. try not to fear it; just give it the respect it deserves and you won't get ***** too badly.
Up-B out of shield. samus players know more than anyone that OoS options come from the most unconventional of moves; DK's best non-grab OoS option is his grounded Up-B.
stage talk
you're both going to live a long time unless you hit him with an offstage dair.
KJ64 and Brinstar are likely DK's CPs against you. Ban whichever you like least; I'd personally ban Brinstar against a good DK player.
where you go to if you lose is going to depend on why you lost in the first place and where you're most comfortable fighting against the type of character DK is. Samus might benefit from Pokémon Stadium's platforms or Dreamland's size for Samus to control the stage with. Use your own judgment on this.
