There's so many echo fighters they can choose it's crazy. I'm hoping for a Pokemon Trainer one. I don't know which generation character they would use but it would be awesome.
I think Pokemon Trainer would be kind of difficult to do cause they'd have to find an echo for all three of them. Can't really think of one for all three.
I think Ms. Pacman is a definite. Shadow is possible. Chrom for Ike. Maybe Ken for Ryu. Gooey for Kirby? Those are the ones that jump out to me.