Technically there's Magolor, but he's been more of a trickster than a true villain ever since Kirby knocked some sense into him. Still, after Bandana Dee, Magolor's my next Kirby pick.Frankly, if Sakurai's classic game bias is the end all know all? I'd be down to get Dark Matter (Swordsmen) as a fighter.
Just thinking of the possibilities, in case other options are considered. I never got the hype surrounding Marx either, if we're talking about marketable characters, wouldn't their best choice be a recent baddie, like the mage sisters or hyness? Morpho Knight?