Yeah, from what little I've played Ness, I did notice that he struggles against disjointed characters like the swordies. Fortunately, I can say that Greninja does a lot better but it requires precise timing and spacing of his Fair to beat out Marth/Lucina and Chrom's aerials. I love how ppl forget that Greninja has a sword of his own. ;P Watch your opponent carefully to decide whether you need a pressuring Fair or a retreating Fair to snuff their approach. Another thing I love about Greninja is that if you can ever get Chrom off stage, you automatically win. Just stand at the ledge and use Substitute when he tries to recover. He can't snap the ledge and if you angle your counter down and away from the stage then he's toast. Also practice shooting your water shuriken in midair to snipe their short hops and use that speed to your advantage. To quote Venia, "A greninja is only as good as their movement."