During today's Smash Bros. Ultimate Nintendo Direct, it was announced that Chrom and Dark Samus will be playable characters – but only as echo fighters.
Chrom appears as an echo fighter of Lucina, and Dark Samus is, unsurprisingly, an echo fighter of Samus. While the fighters will not differ mechanically very much, they'll look different for sure.
Smash Bros. Ultimate releases December 7th 2018 on Switch. Read everything else that was announced during the Direct right here.