If we are bringing in third party characters, im surprised nobody mentioned this, theres a sequel coming out and everything soon. What about gabriel from castlevania? (the new reboot) I think he would fit in well, could just be me . At least i havent seen him mentioned here before.
the newer one is a reboot of the series and they are trying to balance them across every series now, but i agree the older ones would be more nintendo. I liked the game and i think he would have a lot of interesting moves to put in the game. Like his power punch could be like canon or captain falcon from smash bros xD. He could be a really interesting character to add if they got him right.