Whoever the newcomer is, I just want to remind you all to keep an open mind. I'm not Greninja's biggest fan myself - the frog looks weird and its tongue scarf is gross - but I won't lie, they did a really good job at incorporating him into Smash Brothers.
I know there's a lot of people out there who really dislike Incineroar's design for whatever reason. That's fine. But if it is him, try to see what people like about him and try to be respectful about it. The same goes for Isaac - if you go in thinking he'll just be another "anime swordsman" that's what you're going to see.
Throwing a fit over a character you don't like isn't healthy for you and it certainly isn't healthy for the community as a whole. So whatever happens, even if it's Goku or Shrek or whoever else, remember that the game has over 70 other characters to play as and counting and not every one of them is going to realistically appeal to you. But they all have their own fans, so let them have it.